pcu_sock.c: Call osmo_fd_unregister() before closing and changing bfd->fd

Change-Id: I462eea5c44cbffa7fa47121c85fb6ef55394953d
diff --git a/openbsc/src/libbsc/pcu_sock.c b/openbsc/src/libbsc/pcu_sock.c
index 4411df8..aa794de 100644
--- a/openbsc/src/libbsc/pcu_sock.c
+++ b/openbsc/src/libbsc/pcu_sock.c
@@ -502,9 +502,9 @@
 
 	LOGP(DPCU, LOGL_NOTICE, "PCU socket has LOST connection\n");
 
+	osmo_fd_unregister(bfd);
 	close(bfd->fd);
 	bfd->fd = -1;
-	osmo_fd_unregister(bfd);
 
 	/* re-enable the generation of ACCEPT for new connections */
 	state->listen_bfd.when |= OSMO_FD_READ;