src/gsmtap_util.c: fix possible memleak in gsmtap_source_init()

In gsmtap_source_init() we dynamically allocate a gsmtap_inst struct,
but don't free it if the subsequent call to osmo_fd_register() fails.

Change-Id: I970b493f3a64fbe9c3f68fcfba5097ee3ff72960

src/gsmtap_util.c

@@ -440,6 +440,7 @@ struct gsmtap_inst *gsmtap_source_init(const char *host, uint16_t port,
 
 		rc = osmo_fd_register(&gti->wq.bfd);
 		if (rc < 0) {
+			talloc_free(gti);
 			close(fd);
 			return NULL;
 		}