VTCP_Check() to accept ETIMEDOUT on all platforms

it was already accepted on Solaris and NetBSD, now we have seen it on
Linux and I think it does not make sense to keep the exception for
Apple.

Fixes #3532 (hopefully)

lib/libvarnish/vtcp.c

@@ -600,6 +600,10 @@ VTCP_Check(ssize_t a)
 	 * described in the socket(7) manpage.) */
 	if (errno == EAGAIN || errno == EWOULDBLOCK)
 		return (1);
+	/* tcp(7): The other end didn't acknowledge retransmitted data after
+	 * some time. */
+	if (errno == ETIMEDOUT)
+		return (1);
 #if (defined (__SVR4) && defined (__sun))
 	if (errno == ECONNREFUSED)	// in r02702.vtc
 		return (1);