ril: set initial value to GW timingAdvance

RIL_SignalStrength_v10 not support gw.timingAdvance. But default 0 will
be taken as valid value. Set to INT_MAX as invalid value.

Bug: 123096279
Test: Build pass. Correct value for GW timingAdvance in radio log.
01-22 16:22:41.150  1779  1910 V RILJ    : [UNSL]< UNSOL_SIGNAL_STRENGTH
SignalStrength:{ mGsm=CellSignalStrengthGsm: rssi=2147483647 ber=99 mTa=2147483647

Change-Id: I37cc2c246d045a07ffad863fb0cc852d8184c3ca
1 file changed