res_rtp_asterisk: Fix wrongful use of USE_PJPROJECT define.

As pjproject is now used as a shared library a different define,
HAVE_PJPROJECT, is used to specify if pjproject is present.

ASTERISK-24830 #close
Reported by: Stefan Engström


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@432614 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_rtp_asterisk.c

@@ -4994,7 +4994,7 @@ static int ast_rtp_activate(struct ast_rtp_instance *instance)
 	struct ast_rtp *rtp = ast_rtp_instance_get_data(instance);
 
 	/* If ICE negotiation is enabled the DTLS Handshake will be performed upon completion of it */
-#ifdef USE_PJPROJECT
+#ifdef HAVE_PJPROJECT
 	if (rtp->ice) {
 		return 0;
 	}