[Serusers] optimize the mediaproxy when both SIP UA are behind the same NAT clouds.

[szj]

   I tested the SER+Mediaproxy yesterday, well it works
well after i tried many times with SER+RTPProxy. Please
forgive my stupidness.:(.
  But what I want to say is that nathelper can detect such
situations when both SIP UA are behind the same NAT. If
that, the SER can append old media IP and port to the tail
of the SDP, the UA with NATed extentions can communicate
with the other without natproxy helper. I wonder whether
mediaproxy can achieve that goal if the author likes to do
that. I think it is very easy for them if they had enough
time.
  I am glad to hear your advice and responses
  Best Regards.
SunZJ