nfs_bioread_check_cons(). This is required since it is possible
for the vnode to be vgonel()'d while in nfs_upgrade_vnlock() when
a forced dismount is in progress. Also, move the check for VI_DOOMED
in nfs_vinvalbuf() down to after nfs_upgrade_vnlock() and replace the
out of date comment for it.
Submitted by: jhb
Tested by: pho
Approved by: kib (mentor)
MFC after: 1 month
3d458aebb2