improve a calculation method for LTE antenna reception level

This proposal will fix a problem that Android devices could
show different levels of antenna bars under the same radio
environment if each device uses different modem.
This behavior makes confusion toward users and others.

That behavior comes from using RSSNR as a metric for
determining antenna bars. Unfortunately, RSSNR does NOT define
performance requirements and error tolerance level in 3GPP.
Therefore, accuracy of RSSNR measurement could be inconsistent
among Android devices or modems.

The patch we would like to contribute here will be offering
Android device to use RSRQ for antenna bar metric instead of RSSNR.

1.)RSRQ, like RSSNR, takes interference into account
   when measuring the radio quality.
   Android already supports measurement of RSRQ.

2.)The performance requirement for RSRQ is already defined in 3GPP.

3.)DOCOMO and other many mobile operators use RSRP and RSRQ
   when designing LTE coverage areas, and alignment here will
   be very beneficial for both users and operators.

Hope this patch helps to improve Android antenna bar accuracy and consistency today.

Change-Id: Id1c3339764294ef51365ab133a1c7b42e14e1800
Signed-off-by: Kensuke Ueda <uedake@nttdocomo.co.jp>