Don't hang up a call on an SRTP unprotect failure

Also make it more obvious when there is an issue en/decrypting.

(closes issue #17563)
Reported by: Alexcr
Patches: 
      res_srtp.c.patch uploaded by sfritsch (license 1089)
Tested by: twilson


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@287056 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_srtp.c

@@ -343,7 +343,8 @@ static int ast_srtp_unprotect(struct ast_srtp *srtp, void *buf, int *len, int rt
 	}
 
 	if (res != err_status_ok && res != err_status_replay_fail ) {
-		ast_debug(1, "SRTP unprotect: %s\n", srtp_errstr(res));
+		ast_log(LOG_WARNING, "SRTP unprotect: %s\n", srtp_errstr(res));
+		errno = EAGAIN;
 		return -1;
 	}
 
@@ -361,7 +362,7 @@ static int ast_srtp_protect(struct ast_srtp *srtp, void **buf, int *len, int rtc
 	memcpy(srtp->buf, *buf, *len);
 
 	if ((res = rtcp ? srtp_protect_rtcp(srtp->session, srtp->buf, len) : srtp_protect(srtp->session, srtp->buf, len)) != err_status_ok && res != err_status_replay_fail) {
-		ast_debug(1, "SRTP protect: %s\n", srtp_errstr(res));
+		ast_log(LOG_WARNING, "SRTP protect: %s\n", srtp_errstr(res));
 		return -1;
 	}