Don't specify MTU in tc add class commands unless necessary

git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@5896 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb

Shorewall-perl/prog.functions

@@ -150,3 +150,18 @@ restore_dynamic_rules() {
     fi
 }
 
+get_device_mtu1() # $1 = device
+{
+    local output="$(ip link ls dev $1 2> /dev/null)" # quotes required for /bin/ash
+    local mtu
+
+    if [ -n "$output" ]; then
+	mtu=$(find_mtu $output)
+    else
+	return
+    fi
+
+    if [ -n "$mtu" ]; then
+	[ $mtu = 1500 ] || echo mtu $(($mtu + 100))
+    fi
+}