Provide a statistic to track the number of drops in each of the port's
txq's buf_ring.  The aggregate for all the queues of a port is already
provided in ifnet->if_snd.ifq_drops.

MFC after:	3 days.
Remove unused file.
route_output() always supplies info with RTAX_GATEWAY member that
points to a sockaddr of AF_LINK family. Assert this instead of
checking.
Fix installworld when nmtree is not on the host by only adding it to
ITOOLS when we will be using the host copy.

Fix installkernel when -DNO_ROOT is set.
Log the addition of login.conf.db, passwd, pwd.db, and spwd.db via cat -l.

Make cat a bootstrap tool to facilitate this.