Avoid refcnt underrun on xprt stall.

Do not release dispatch xprt ref on stall return from
nfs_rpc_cond_stall_xprt, as it protects rechability from
the stallq itself.

The stall thread appears to do the right thing, returning
its own reference, after first re-arming EPOLL.

This change (I believe) implements the fix
proposed by Shyamsundar Ranganathan <srangana@redhat.com>,
in reporting this issue.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Cleanup killed cache entries inline.

Removes cleanup queue processing from lru_run, in favor
of inline cleanup on return of last ref.

Also, change the order of cih_remove_checked and cleanup push
operations in cache_inode_kill entry.

It also appears that the (removed) cleanup processing incorrectly
returned a cache entry reference.  This likely resulted in leaks
and use-after-free conditions.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>