Changes

gprs_ns2_sns: add include osmocom/core/talloc.h

Talloc is directly used, do an explicit include talloc
and not depend on a another header to include it.

Change-Id: I867c5e3f87efcf5bcc99713a0c1dcaecfc55fcbd

gprs_ns2_sns: do_sns_add: ensure ip4/ip6 pointer is set

To make clang analyser happy. It is also a good check, to ensure the
correct address contains valida data

Change-Id: I22c0096dca75bc69cdf396b240ac590d949eeb0a

gprs_ns2_sns: move the NS-ALIVE PDU of a new NS-VC after the SNS-ACK

When adding a new NS-VC after the SNS-CONFIG is done, the new NS-VC would send out a
NS-ALIVE before sending out the SNS-ACK towards the remote NSE.
This isn't a big issue, because the SNS-ACK can be reordered by the network anyways,
but be nice and ensure the order matches the expectation.

Related: OS#6611
Change-Id: I6503bbb32b4440eb53f8c9bd03572f4a189f1a86

gprs_ns2_sns: improve search for same NS-VC

Adding a second NS-VC with the same IP+UDP isn't possible,
even when the weights are different, because the NS-ALIVE wouldn't work.
Also a NS-VC is identified by IP+UDP and not by the weights.

IPv6 did this already. Use the same logic for IPv4.
Further relax the search of NS-VC when removing NS-VC. Only take care
of IP+UDP and ignore signalling weight and data weights.

Related: OS#6611
Change-Id: Ibbc1a794a9a9f0ce6e583fd9743e7f02d52a99cf

gprs_ns2_sns: fix error cases of SNS_ADD

When adding a NS-VC fails, the SNS-ACK with failure code should follow,
but no second SNS-ACK.

Related: OS#6611
Change-Id: I06bc2622f89256d9675e29b49acc7a3e0647eeae