BSD: Detect initial link state in ifa_data

BSD: Detect initial link state in ifa_data

Not all interfaces report media state to get the link state.
However, link state is available from getifaddrs(3) ifa_data
for AF_LINK addresses.

Testing shows that link state is also sent correctly via
route(4) messages for the same interface.

This makes pppoe(4) interfaces more reliable on FreeBSD and OpenBSD.