xtables-addons: rtsp: support destination format address:port

xtables-addons: rtsp: support destination format address:port

RFC2326 specifies the attribute client_port as the RTP/RTCP port pair on
which the client has chosen to receive media data and control info;
however some clients (mostly STBs) embed the client_port value in the
destination attribute in the form of destination=<address:port> without
specifying the client_port attribute in the SETUP message.
To support such clients check if the destination attribute contains a
port value and use it as port value for the expected RTP connection.

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>