Add link status descriptions and related structures for userland applications.
Add link status descriptions and related structures for userland
applications.

Open[BGP|OSPF]D make use of this to determine the link status of
interfaces to make the right routing descisions.

Obtained from:	OpenBSD
MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase