gb: Add functions to access the LL part of the NS-VC objects

Adds the functions gprs_ns_ll_copy() and gprs_ns_ll_clear(). Renames
gprs_ns_format_peer() to gprs_ns_ll_str(). All of these functions
uniformly access the link layer part within the NS-VC objects.

Sponsored-by: On-Waves ehf
4 files changed