#33 Allow different payload number in SDP answer

[Andreas Piirimets]

RFC 3264 states that:

"In the case of RTP, if a particular codec was referenced
with a specific payload type number in the offer, that
same payload type number SHOULD be used for that
codec in the answer. Even if the same payload type
number is used, the answer MUST contain rtpmap
attributes to define the payload type mappings for
dynamic payload types, and SHOULD contain mappings
for static payload types. "

If SIPcon1 sends an INVITE with a specific payload type
number for a media, it expects the same number to be
returned in the 200 OK's SDP. This follows the SHOULD
rule above.

SIPcon1 should also be able to handle different payload
type numbers in the answer. This should be
implemented.