zebra: ifi_link_state is the link state

zebra: ifi_link_state is the link state

SIOCGIFMEDIA returns the media state.
SIOCGIFDATA returns interface data which includes the link state.

While the status of the former is usually indicitive of the latter,
this is not always the case.
Ifact some recent net80211 changes in at least NetBSD and OpenBSD
have MONITOR media set to active but the link status set to DOWN.

All interfaces will return link state with SIOCGIFDATA, unlike
SIOCGIFMEDIA. However not all BSD's support SIOCGIFDATA - it has
recently been accepted into FreeBSD-13.
However, all BSD's do report the same structure in ifa_data for
AF_LINK addresses from getifaddrs(3) so the information has always
been available.

Signed-off-by: Roy Marples <roy@marples.name>