Accept all ENET* ECONN* EHOST* errnos

... documented on Linux as POSIX.1

The exception here is ECONNREFUSED which so far we only tolerate for
Solaris and which seems to make sense for connect() only.

To be discussed in #3539

lib/libvarnish/vtcp.c

@@ -604,6 +604,13 @@ VTCP_Check(ssize_t a)
 	 * some time. */
 	if (errno == ETIMEDOUT)
 		return (1);
+	/* #3539 various errnos documented on linux as POSIX.1 */
+	if (errno == ENETDOWN || errno == ENETUNREACH || errno == ENETRESET ||
+	    errno == ECONNABORTED || /* ECONNRESET see above */
+	    errno == EHOSTUNREACH || errno == EHOSTDOWN) {
+		return (1);
+	}
+
 #if (defined (__SVR4) && defined (__sun))
 	if (errno == ECONNREFUSED)	// in r02702.vtc
 		return (1);