udp: Allow specifying multicast include/blocks as host names as well

Previously this only allowed literal IP addresses. When these
are conveyed in a SDP file as in RFC4570, host names are allowed
as well.

Signed-off-by: Martin Storsjö <martin@martin.st>
udp: Keep track of include and exclude sources separately

This allows us to explicitly fail if the caller tried to set
both inclusions and exclusions at the same time.

Signed-off-by: Martin Storsjö <martin@martin.st>
rtpproto: Support more than one SSM include address, support excludes

Signed-off-by: Martin Storsjö <martin@martin.st>
rtsp: Support RFC4570 (source specific multicast) more properly.

Add support for domain names, for multiple source addresses,
for exclusions, and for session level specification of addresses.

Signed-off-by: Martin Storsjö <martin@martin.st>