Add same padding to mobile datatype as wifi

SignalCluster view used to have a start-margin of 2.5dp, so now both the
wifi icon and the mobile data indicator need that padding (because you
will only ever see the data type indicator if wifi is not on.

Test: visual
Change-Id: I7b34fd80eb222610fc7df76be7a76c0f5f6e0fbb
Fixes: 110225644