The kernel and libnl adds two new flags IFA_F_MANAGETEMPADDR
and IFA_F_NOPREFIXROUTE. Older versions of libnl do not recognize
this flag, so add a workaround to nm_platform_ip6_address_to_string()
to show "mngtmpaddr" and "noprefixroute", respectively.

Also, add function nm_platform_check_support_libnl_extended_ifa_flags()
that checks whether libnl supports extended ifa_flags that were
added recently.

Extended flags and the two ifa-flags above were added to libnl in close
succession.

Signed-off-by: Thomas Haller <thaller@redhat.com>