abis_nm: Support parsing nanoBTS format for Get Attributes Info

Spec compliant format is defined in:
* 3GPP TS 52.021 §8.11.3 "Get Attribute Response"
* 3GPP TS 52.021 §9.4.64 "Get Attribute Response Info".

On nanoBTS, however, reported attribute list is provided directly inside/after
the foh header instead of being enveloped inside the Get Attributes Response Info.
Furthermore, The Get Attributes Response Info can still appear and be at any position
in the reported attribute list, and it only contains the unreported
attribute ID list inside.

Change-Id: I81a613d53bddf432a79fa5cb0bf9d847b4bdee37
1 file changed