sip codec negotiation of dynamic rtp payloads error fix

This patch fixes how chan_sip handles dynamic rtp payload types
it does not understand.  At the moment if a dynamic payload's mime
type does not match one we understand, the payload does not get
removed from our payload table.  As a result of this, the payload
is set to whatever dynamic codec we use internally for that payload
number on outgoing INVITES.  This is incorrect.

This patch fixes this by properly checking the rtpmap set function's
return code to make sure it was found.  The function can return both
-1 and -2 depending on the source of the mismatch.  We were just
checking -1 explicitly.

Review: https://reviewboard.asterisk.org/r/1169/



git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@314017 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/rtp_engine.h

@@ -964,7 +964,8 @@ void ast_rtp_codecs_payloads_set_m_type(struct ast_rtp_codecs *codecs, struct as
  * \param options Optional options that may change the behavior of this specific payload
  *
  * \retval 0 success
- * \retval -1 failure
+ * \retval -1 failure, invalid payload numbe
+ * \retval -2 failure, unknown mimetype
  *
  * Example usage:
  *