Changes

abis_osmo: Fix reading Abis IPA OSMO_EXT type

The l2 buffer points to the IPA payload, not the the ext type.
This was probably not the case during initial development of the stack,
but it is since a while ago, to be inline with usual behavior of ipa
handling.

This patch fixes BTS_Tests_OML.TC_ipa_osmo_pcu_anr_fwd failure.

Change-Id: I4941d28b2416a70e61d2881e8ebc556c5421256c