get rid of ->mnt_longterm

it's enough to set ->mnt_ns of internal vfsmounts to something
distinct from all struct mnt_namespace out there; then we can
just use the check for ->mnt_ns != NULL in the fast path of
mntput_no_expire()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc fs/dcache.c
Simple merge

diff --cc fs/fs_struct.c
Simple merge

diff --cc fs/internal.h
Simple merge

diff --cc fs/mount.h
Simple merge

diff --cc fs/namespace.c
Simple merge