ipa_server_conn: Add remote (peer) address to struct

This is better than every implementation calling getpeername()
on its own.
diff --git a/include/osmocom/abis/ipa.h b/include/osmocom/abis/ipa.h
index 6e9f9dd..6447ccd 100644
--- a/include/osmocom/abis/ipa.h
+++ b/include/osmocom/abis/ipa.h
@@ -38,6 +38,9 @@
 	int (*cb)(struct ipa_server_conn *peer, struct msgb *msg);
 	void				*data;
 	struct msgb			*pending_msg;
+	/* remote address information */
+	const char			*addr;
+	uint16_t			port;
 };
 
 struct ipa_server_conn *