Add support for multiple APN profiles for subscriber data

Previous the HLR sent in the Insert Subscriber Data call only the
wildcard APN as a single entry.
This violates the spec because the first entry (with the lowest context_id) is
always the default APN, but it is forbidden to have a wildcard APN as default apn.

Introduce a default template/profile which can contain multiple APNs.
This profile is always sent out to the SGSN/MME as part of Insert-Subscriber-Data.
In the future a subscriber might have a profile template name written into the
database which will resolve to a "pdp-profile premium" in the configuration.

To be backward compatible, if the pdp-profile default section is missing,
the HLR will send out only a wildcard APN.

Config example:

hlr
 ps
  pdp-profile default
   profile 1
    apn internet
   profile 2
    apn *

Changes to the apn list will be only handed out to subscribers
when the subscriber do a location update.

Related: SYS#6391
Change-Id: I540132ee5dcfd09f4816e02e702927e1074ca50f
---
M doc/examples/osmo-hlr.cfg
M include/osmocom/hlr/hlr.h
A include/osmocom/hlr/hlr_ps.h
M include/osmocom/hlr/hlr_vty.h
M src/gsup_server.c
M src/hlr_vty.c
M tests/test_nodes.vty
M tests/test_subscriber_errors.ctrl
8 files changed, 330 insertions(+), 14 deletions(-)