ipaccess: hack to get openBSC's ipaccess-config tool working

Export one function that we shouldn't, it's a quick way to fix
the ipaccess-config in openBSC.
diff --git a/include/osmocom/abis/ipaccess.h b/include/osmocom/abis/ipaccess.h
index 7083ce9..1999fa4 100644
--- a/include/osmocom/abis/ipaccess.h
+++ b/include/osmocom/abis/ipaccess.h
@@ -108,4 +108,7 @@
 	uint64_t serno;
 };
 
+/* quick solution to get openBSC's ipaccess tools working. */
+int ipaccess_fd_cb(struct osmo_fd *bfd, unsigned int what);
+
 #endif /* _OSMO_PROTO_IPACCESS_H */