opening the POSIX fifo; convert ENXIO error returns to EOPNOTSUPP.
This improves handling of the case where the /var/run/lock fifo exists
but there is no listener: we immediately return EOPNOTSUPP rather
than blocking until a listener turns up. This could occur during a
diskless boot before rpc.lockd is loaded, or if the lock file persists
across a reboot following the disabling of rpc.lockd. This may have
suddenly started to occur due to fifo blocking fixes--previously it
looks like attempts to read on a fifo with no listener would time out
due to insufficient resources.
Reviewed by: alfred
847b14bd3c