mount.nfs: Move start_statd into nfs_mount

Move start_startd into network.c, and move the call inside of
nfs_mount, instead of immediately after - conceptually a better place
for it.

Also fix a minor nit:  Since the mount actually fails if start_statd
doesn't work, cause mount.nfs to exit with a status of EX_FAIL.

Still need to do something about "running_bg" in nfsmount.c:nfsmount().

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Neil Brown <neilb@suse.de>