wifi: Allow Settings to retrieve country code (1/2)

This makes getCountryCode behave like getFrequencyBand

This allows Settings to get/set country code like
it can for frequency band.

Ported from cm-10.2, adjusted for 4.4
Settings part: http://review.cyanogenmod.org/54904

Change-Id: Id9f00d3a678642c6c142fd1511af820d729507a7