Shorten gwifip if whole socket path exceeds 100 chars

dpinger stopps with an error when the socketname exceeds over
(around) 100 characters. The dpinger will not start and not deliver
monitoring results to the WebUI.

These long socket names can get created when using link-local addresses
and long gateway names / interface scopes.

See Ticket 6505

src/etc/inc/gwlb.inc

@@ -130,8 +130,19 @@ function start_dpinger($gateway) {
 
 	$pidfile = "{$g['varrun_path']}/dpinger_{$gateway['name']}~" .
 	    "{$gateway['gwifip']}~{$gateway['monitor']}.pid";
+	# dpinger socket path should not be longer then uaddr.sun_path
+	if (strlen($pidfile) > 100) {
+		$pidfile = "{$g['varrun_path']}/dpinger_{$gateway['name']}~" .
+		    substr(md5($gateway['gwifip']),0,8) . "~" .
+		    $gateway['monitor'] . ".pid";
+	}
 	$socket = "{$g['varrun_path']}/dpinger_{$gateway['name']}~" .
 	    "{$gateway['gwifip']}~{$gateway['monitor']}.sock";
+	if (strlen($socket) > 100) {
+		$socket = "{$g['varrun_path']}/dpinger_{$gateway['name']}~" .
+		    substr(md5($gateway['gwifip']),0,8) . "~" .
+		    $gateway['monitor'] . ".sock";
+	}
 	$alarm_cmd = "{$g['etc_path']}/rc.gateway_alarm";
 
 	$params  = "-S ";			/* Log warnings via syslog */