Use OpenSSL instead of the internal crypto backend. Everything in
OpenWrt that links to libsrtp2 depends on OpenSSL anyway.
Upsides:
- the libsrtp2 package size shrinks a bit (for example from 35 to 24
KiB on ath79)
- allows to use more cipher suites
- may allow for hardware acceleration
Closes#763
Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>
9b9ef7ff84