Added temporal clamp_tcpmss script to solve tcp mtu/mss problem with lan clients

packages/qmp-small-node/files/etc/uci-defaults/qmp_clamp_tcpmss

+#!/bin/sh
+
+if cat /etc/firewall.user | grep -e "^# Clamp MSS TCP rule to fix MTU problems"; then exit 0; fi
+
+cat << EOF >> /etc/firewall.user
+# Clamp MSS TCP rule to fix MTU problems
+iptables -A FORWARD -p tcp -i br-lan ! -d 10.0.0.0/8  -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
+EOF