telephony: SignalStrengh: Don't calculate a LTE snr if the srq is invalid

If the previous values are invalid and signal quality is -1, chances are there's
no LTE signal at all, so don't calculate the SNR and mark it invalid as well.

This fixes the strength indicator in GSM devices where it was being skewed
by the ghost LTE value

Change-Id: I070573401c141aa99941a332ee256246697abb90
implement noise suppression for phone calls (1/2)

Change-Id: If51532bd8220fab8722bbb594f70515f9d74b49b
Switch to new handling of public symbols
Get rid of .DS_Store!