nfsd4: fix recovery-dir leak on nfsd startup failure

The current code never calls nfsd4_shutdown_recdir if nfs4_state_start
returns an error. Also, it's better to go ahead and consolidate these
functions since one is just a trivial wrapper around the other.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>