parser: new internal msg flag FL_SDP_BODY

- mark the request if there is an sdp body (useful for multi-part bodies
  or to quickly check in tm routes as the msg body is not cloned in shm
  and will require parsing again)

parser/msg_parser.h

@@ -118,6 +118,7 @@ enum request_method {
 #define FL_MTU_TLS_FB   (1 << 9)
 #define FL_MTU_SCTP_FB  (1 << 10)
 #define FL_ADD_LOCAL_RPORT  (1 << 11) /*!< add 'rport' to local via hdr */
+#define FL_SDP_BODY     (1 << 12)  /*!< msg has SDP in body */
 
 /* WARNING: Value (1 << 29) is temporarily reserved for use in kamailio acc
  * module (flag FL_REQ_UPSTREAM)! */