chan_sip: Don't send trailing \0 on keep alive packets

This is a partial fix for ASTERISK~25817 but does not address the
comments regarding RFC 5626.

Change-Id: I227e2d10c0035bbfa1c6e46ae2318fd1122d8420

channels/chan_sip.c

@@ -30125,6 +30125,7 @@ static int sip_send_keepalive(const void *data)
 	struct sip_peer *peer = (struct sip_peer*) data;
 	int res = 0;
 	const char keepalive[] = "\r\n";
+	size_t count = sizeof(keepalive) - 1;
 
 	peer->keepalivesend = -1;
 
@@ -30135,12 +30136,12 @@ static int sip_send_keepalive(const void *data)
 
 	/* Send the packet out using the proper method for this peer */
 	if ((peer->socket.fd != -1) && (peer->socket.type == AST_TRANSPORT_UDP)) {
-		res = ast_sendto(peer->socket.fd, keepalive, sizeof(keepalive), 0, &peer->addr);
+		res = ast_sendto(peer->socket.fd, keepalive, count, 0, &peer->addr);
 	} else if ((peer->socket.type & (AST_TRANSPORT_TCP | AST_TRANSPORT_TLS)) &&
 		   peer->socket.tcptls_session) {
-		res = sip_tcptls_write(peer->socket.tcptls_session, keepalive, sizeof(keepalive));
+		res = sip_tcptls_write(peer->socket.tcptls_session, keepalive, count);
 	} else if (peer->socket.type == AST_TRANSPORT_UDP) {
-		res = ast_sendto(sipsock, keepalive, sizeof(keepalive), 0, &peer->addr);
+		res = ast_sendto(sipsock, keepalive, count, 0, &peer->addr);
 	}
 
 	if (res == -1) {
@@ -30154,7 +30155,7 @@ static int sip_send_keepalive(const void *data)
 		}
 	}
 
-	if (res != sizeof(keepalive)) {
+	if (res != count) {
 		ast_log(LOG_WARNING, "sip_send_keepalive to %s returned %d: %s\n", ast_sockaddr_stringify(&peer->addr), res, strerror(errno));
 	}