server_conn_fsm_alloc(): add explicit talloc context argument

The rspro_server_conn might be a static member of a different struct
and hence not suitable as a talloc context.

Change-Id: I9fd78d558f791d452f2a5279f1af13fd596c1cd6
diff --git a/src/client.h b/src/client.h
index 7a3c476..d85e647 100644
--- a/src/client.h
+++ b/src/client.h
@@ -37,6 +37,7 @@
 	uint16_t server_port;
 };
 
+int server_conn_fsm_alloc(void *ctx, struct rspro_server_conn *srvc);
 extern struct osmo_fsm remsim_client_server_fsm;
 
 /* main.c */