rtpproxy patches

[Daniel Pocock]

Hi Maxim,

I've been working with your rtpproxy code.  I am currently running 0.2 
and I have reviewed the 0.3-1 source as well.

I've made the following changes which apply to both versions, would you 
be interested in using these?

a) rtpp_session.ttl is now an array
  rtpp_session.ttl[0] represents the ttl for caller
  rtpp_session.ttl[1] represents the ttl for callee
  If either ttl reaches 0, session is dropped

b) the command line parameter `-m unix:socket' allows the user to 
specify a socket that will be notified whenever a session timeout 
occurs.  The port numbers will be written to the socket.  The socket 
must be created by some other application, if the socket doesn't exist 
then rtpproxy will continue anyway and send a warning to the log.

Change (a) is something that some people might want to vary - some users 
may want to revert to old behaviour.  I can add a command line option 
for reverting to the old behaviour.

Regards,

Daniel