android: configs: Reorder config fragments, update README

Change-Id: I5ee4b794dcc00f74f26562e49a406ea292af63ee
android: configs: require TCPMSS, remove SCHED_TRACER and TIMER_STATS

TCPMSS is required for the Android Vpn service to correctly
handle the MTU on tun/ppp devices.  Bug: 11579326
We don't really need SCHED_TRACER and the TIMER_STATS.

Change-Id: I10c5767a6324a496713752d4fe9eff361dc8e06a