hlr: Don't attempt to find AUTN in 2G-only tuple

In Change-Id I40c6cf7e28ad9331e6c27fe7acafa3f9e277eedf we introduced
a patch that verifies the AMF separation bit for 3G/3G vs 4G
authentication.  However, the test ignored the fact that AUTN cannot
be present in pure 2G tuples.

This makes TC_gsup_sai pass again.

Change-Id: I9b61e62a58b583461dd5e67dd12119be282cae21
1 file changed