res_pjsip_asterisk.c: Fix compile error if libsrtp is not installed.

struct ast_rtcp does not define the dtls member if SRTP is not enabled.

ASTERISK-26732

Change-Id: Id15ea212e04490e012f2cf4a56818b4dd948875e

res/res_rtp_asterisk.c

@@ -5017,7 +5017,9 @@ static void ast_rtp_prop_set(struct ast_rtp_instance *instance, enum ast_rtp_pro
 					return;
 				}
 				rtp->rtcp->s = -1;
+#ifdef HAVE_OPENSSL_SRTP
 				rtp->rtcp->dtls.timeout_timer = -1;
+#endif
 				rtp->rtcp->schedid = -1;
 			}