res_rtp_asterisk: Avoid close the rtp/rtcp fd twice.

When RTCP-MUX enabled. rtp->s is the same as rtcp->s, check this before
close the file descriptor. Close the FD twice will hangs the asterisk
under heavy load.

ASTERISK-27299 #close
Reported-by: Aaron An
Tested-by: AaronAn

Change-Id: I870a072d73fd207463ac116ef97100addbc0820a

res/res_rtp_asterisk.c

@@ -3247,7 +3247,9 @@ static int ast_rtp_destroy(struct ast_rtp_instance *instance)
 		 * entry at this point since it holds a reference to the
 		 * RTP instance while it's active.
 		 */
-		close(rtp->rtcp->s);
+		if (rtp->rtcp->s > -1 && rtp->s != rtp->rtcp->s) {
+			close(rtp->rtcp->s);
+		}
 		ast_free(rtp->rtcp->local_addr_str);
 		ast_free(rtp->rtcp);
 	}