Stop after first timeout error

Fixing IPV4 error for dualstack cluster without IPV6 connectivity jackc#139

pgconn.go

@@ -188,6 +188,10 @@ func ConnectConfig(octx context.Context, config *Config) (pgConn *PgConn, err er
 			if _, ok := cerr.err.(*NotPreferredError); ok {
 				fallbackConfig = fc
 			}
+			if _, ok := cerr.err.(*errTimeout); ok {
+				// once we reach timeout it's useless to check other fallbacks
+				break
+			}
 		}
 	}