chan_sip: Remember SDP negotiation on SIP_CODEC_INBOUND.

chan_sip: Remember SDP negotiation on SIP_CODEC_INBOUND.

After a SIP_CODEC_INBOUND in the dialplan, do not continue with cached formats
but remember the joint format. Cached formats contain default parameters,
often create an empty fmtp line. However, a joint format might have passed
format_get_joint(.) in a res_format_attr_* module (like Opus Codec) and
contain the resulting format parameters from a SDP negotiation.

ASTERISK-26691 #close

Change-Id: I35712d98a793d4c3efdd156cec57deab9014b1dc