GsmSS: Use data tech in isConcurrentVoiceAndDataAllowed

Voice technology is not properly supported in older RILs

When using RIL blobs, the value would be set to UNKNOWN,
resulting in data being disconnecting during call despite
being on 3G.

When using source-built RIL, the value would be set to
UMTS regardless of 2G/3G status. (At least from reading
the source.)

Change-Id: I12738abc1736165e92aa7f4530ca043cc1acc44d