This commit adds the exported functions apn_ctx_find_alloc,
apn_ctx_free, apn_ctx_by_name, and apn_ctx_match to manage and
retrieve APN to GGSN mappings.
The following VTY commands are added to 'config-sgsn':
- apn APN ggsn <0-255>
- apn APN imsi-prefix PREFIX ggsn <0-255>
which maps an APN gateway string to an SGSN id. The SGSN must be
configured in advance. When matching an APN string, entries with a
leading '*' are used for suffix matching, otherwise an exact match is
done. When a prefix is given, it is matched against the IMSI. If
several entries match, a longer matching IMSI prefix has precedence.
If there are several matching entries with the same PREFIX, the entry
with longest matching APN is returned.
Ticket: OW#1334
Sponsored-by: On-Waves ehf
cb1db8b6d5