[core] Fixed group import option.
SRTO_CONNTIMEO, SRTO_PAYLOADSIZE, SRTO_PBKEYLEN had size autodetection bugs.

[core] Fixed static variable usage in the crypto module (#3047).
Static variable `hcrypt_MsgInfo _hcMsg_SRT_MsgInfo` was declared twice.
There was a mutual dependency between `_hcMsg_SRT_MsgInfo` and `hcryptMsg_SRT_ParseMsg(..)`.

[core] Fixed nonchecked empty config for packetfilter (#3031).

[apps] Fixed compiler warnings (G++ 9.4)

[docs] Fixed API doc: SRT_INVALID_SOCK instead of SRT_ERROR in str_ac…
…cept (#2785).
The functions srt_accept() and srt_accept_bond() return a SRTSOCKET.
In case of error, the returned value is SRT_INVALID_SOCK, not SRT_ERROR.
In practice, the two values are identical (-1) but they do not have
the same semantics.

[apps] Fixed conditional IP_ADD_SOURCE_MEMBERSHIP in testmedia (#2780).

[docs] Minor updates to AEAD docs plus changed v1.6.0 to 1.5.2 in som…
…e files

[core] Correct remaining endianness issues
Fixes the last two remaining test failures on big-endian.  These
operations were all already no-ops on little-endian, and unnecessarily
byteswapped the IP addresses on big-endian.
Closes: #2697

[core] Added rejection handshake sent to the peer in rendezvous mode (#…
…2667).
Fixed: send SHUTDOWN also in blocking mode.
Added fallback ROGUE reject reason case it isn't set.

[API] SRT version raised to 1.5.2.