Make sure that argv[] argument pointers are not modified.

The hush shell dynamically allocates (and re-allocates) memory for the
argument strings in the "char *argv[]" argument vector passed to
commands.  Any code that modifies these pointers will cause serious
corruption of the malloc data structures and crash U-Boot, so make
sure the compiler can check that no such modifications are being done
by changing the code into "char * const argv[]".

This modification is the result of debugging a strange crash caused
after adding a new command, which used the following argument
processing code which has been working perfectly fine in all Unix
systems since version 6 - but not so in U-Boot:

int main (int argc, char **argv)
{
	while (--argc > 0 && **++argv == '-') {
/* ====> */	while (*++*argv) {
			switch (**argv) {
			case 'd':
				debug++;
				break;
			...
			default:
				usage ();
			}
		}
	}
	...
}

The line marked "====>" will corrupt the malloc data structures and
usually cause U-Boot to crash when the next command gets executed by
the shell.  With the modification, the compiler will prevent this with
an
	error: increment of read-only location '*argv'

N.B.: The code above can be trivially rewritten like this:

	while (--argc > 0 && **++argv == '-') {
		char *arg = *argv;
		while (*++arg) {
			switch (*arg) {
			...

Signed-off-by: Wolfgang Denk <wd@denx.de>
Acked-by: Mike Frysinger <vapier@gentoo.org>

common/cmd_net.c

@@ -28,11 +28,11 @@
 #include <command.h>
 #include <net.h>
 
-extern int do_bootm (cmd_tbl_t *, int, int, char *[]);
+extern int do_bootm (cmd_tbl_t *, int, int, char * const []);
 
-static int netboot_common (proto_t, cmd_tbl_t *, int , char *[]);
+static int netboot_common (proto_t, cmd_tbl_t *, int , char * const []);
 
-int do_bootp (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_bootp (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	return netboot_common (BOOTP, cmdtp, argc, argv);
 }
@@ -43,7 +43,7 @@ U_BOOT_CMD(
 	"[loadAddress] [[hostIPaddr:]bootfilename]"
 );
 
-int do_tftpb (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_tftpb (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	return netboot_common (TFTP, cmdtp, argc, argv);
 }
@@ -54,7 +54,7 @@ U_BOOT_CMD(
 	"[loadAddress] [[hostIPaddr:]bootfilename]"
 );
 
-int do_rarpb (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_rarpb (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	return netboot_common (RARP, cmdtp, argc, argv);
 }
@@ -66,7 +66,7 @@ U_BOOT_CMD(
 );
 
 #if defined(CONFIG_CMD_DHCP)
-int do_dhcp (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_dhcp (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	return netboot_common(DHCP, cmdtp, argc, argv);
 }
@@ -79,7 +79,7 @@ U_BOOT_CMD(
 #endif
 
 #if defined(CONFIG_CMD_NFS)
-int do_nfs (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_nfs (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	return netboot_common(NFS, cmdtp, argc, argv);
 }
@@ -151,7 +151,7 @@ static void netboot_update_env (void)
 }
 
 static int
-netboot_common (proto_t proto, cmd_tbl_t *cmdtp, int argc, char *argv[])
+netboot_common (proto_t proto, cmd_tbl_t *cmdtp, int argc, char * const argv[])
 {
 	char *s;
 	char *end;
@@ -230,7 +230,7 @@ netboot_common (proto_t proto, cmd_tbl_t *cmdtp, int argc, char *argv[])
 }
 
 #if defined(CONFIG_CMD_PING)
-int do_ping (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_ping (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	if (argc < 2)
 		return -1;
@@ -280,7 +280,7 @@ static void cdp_update_env(void)
 
 }
 
-int do_cdp (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_cdp (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	int r;
 
@@ -302,7 +302,7 @@ U_BOOT_CMD(
 #endif
 
 #if defined(CONFIG_CMD_SNTP)
-int do_sntp (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_sntp (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	char *toff;
 
@@ -340,7 +340,7 @@ U_BOOT_CMD(
 #endif
 
 #if defined(CONFIG_CMD_DNS)
-int do_dns(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_dns(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	if (argc == 1) {
 		cmd_usage(cmdtp);