ipa: Guard against calling ipa_client_conn_open* multiple times

Change-Id: I574af543429d01c9522e267265e97e4efe55b60c
diff --git a/src/input/ipa.c b/src/input/ipa.c
index 62b21e5..94e7e5a 100644
--- a/src/input/ipa.c
+++ b/src/input/ipa.c
@@ -249,6 +249,9 @@
 {
 	int ret;
 
+	if (link->ofd->fd != -1)
+		return -EINVAL;
+
 	link->state = IPA_CLIENT_LINK_STATE_CONNECTING;
 	ret = osmo_sock_init2(AF_INET, SOCK_STREAM, IPPROTO_TCP,
 			     link->local_addr, link->local_port,