fusion3: Enable iptables TCPMSS

VpnService makes use of this extension in
system/netd/SecondaryTableController.cpp:389 to make sure packet size
does not exceed MTU when tethering is enabled.

Change-Id: I1e21a022c97889a028a717b3fd7dd76e38def806
Merge pull request #3 from CyanogenMod/cm-11.0

fusion3: Enable iptables TCPMSS