u_ether: Boost the cpu when rmnet/rndis ifc is up

During peak throughput testing when threads migrate from cpus
running in peak frequency to cpu running at low frequency there
could be throughput drop. Also, if for some unknown reason
upcoming cpu setttles at lower frequency it could lead throughput
drop. Avoid this by boosting the cpus to 1Ghz whenever usb tethered
call is established. There is no power impact as USB cable is
connected and phone can be charged from phone.

Change-Id: I5d54565752527dbdbed7280fea852fc7bd3e09dd
Signed-off-by: Vamsi Krishna <vskrishn@codeaurora.org>