mgcp: Call osmo_fd_unregister() before closing and changing bfd->fd

Change-Id: I2227e97b1cffab5ab0138ce95a2523a824ec35f0
diff --git a/openbsc/src/libmgcp/mgcp_network.c b/openbsc/src/libmgcp/mgcp_network.c
index e268658..c52bd0b 100644
--- a/openbsc/src/libmgcp/mgcp_network.c
+++ b/openbsc/src/libmgcp/mgcp_network.c
@@ -1050,15 +1050,15 @@
 int mgcp_free_rtp_port(struct mgcp_rtp_end *end)
 {
 	if (end->rtp.fd != -1) {
+		osmo_fd_unregister(&end->rtp);
 		close(end->rtp.fd);
 		end->rtp.fd = -1;
-		osmo_fd_unregister(&end->rtp);
 	}
 
 	if (end->rtcp.fd != -1) {
+		osmo_fd_unregister(&end->rtcp);
 		close(end->rtcp.fd);
 		end->rtcp.fd = -1;
-		osmo_fd_unregister(&end->rtcp);
 	}
 
 	return 0;