MINOR: lua: use conn_get_{src,dst} to retrieve connection addresses

This replaces the previous conn_get_{from,to}_addr() and reuses the
existing error checks.
diff --git a/src/hlua.c b/src/hlua.c
index fe67f04..37d576f 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -2258,8 +2258,7 @@
 		return 1;
 	}
 
-	conn_get_to_addr(conn);
-	if (!(conn->flags & CO_FL_ADDR_TO_SET)) {
+	if (!conn_get_dst(conn)) {
 		xref_unlock(&socket->xref, peer);
 		lua_pushnil(L);
 		return 1;
@@ -2308,8 +2307,7 @@
 		return 1;
 	}
 
-	conn_get_from_addr(conn);
-	if (!(conn->flags & CO_FL_ADDR_FROM_SET)) {
+	if (!conn_get_src(conn)) {
 		xref_unlock(&socket->xref, peer);
 		lua_pushnil(L);
 		return 1;