tlscertificate-gnutls: add support for X509v3 SAN IP addresses

If a network address is given and the IP can not resolve to a hostname
we now check it with the X509v3 Subject Alternate Name IP
fields (GNUTLS_SAN_IPADDRESS).

https://bugzilla.gnome.org/show_bug.cgi?id=726596
tests: updated server certificate and added UT for X509v3 SAN IP

Updated server certificate by adding a X509v3 Subject Alternative Name
using an IP address.

A test case to verify that the IP is a valid identity for that
certificate has been added.

https://bugzilla.gnome.org/show_bug.cgi?id=726596
gnutls: refactor and extend IP altname check

Refactor g_tls_certificate_gnutls_verify_identity() and extend the IP
address altname code to handle GInetSocketAddress identities as well.

Extend tls/tests/certificate.c to check that case as well, and also
check that incorrect IP addresses (as GNetworkAddress or
GInetSocketAddress) fail to verify.