NFSD: Fix nfsd_breaker_owns_lease() return values

These have been incorrect since the function was introduced.

A proper kerneldoc comment is added since this function, though
static, is part of an external interface.
Reported-by: NDai Ngo <dai.ngo@oracle.com>
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -4711,6 +4711,14 @@ nfsd_break_deleg_cb(struct file_lock *fl)
 	return ret;
 }
 
+/**
+ * nfsd_breaker_owns_lease - Check if lease conflict was resolved
+ * @fl: Lock state to check
+ *
+ * Return values:
+ *   %true: Lease conflict was resolved
+ *   %false: Lease conflict was not resolved.
+ */
 static bool nfsd_breaker_owns_lease(struct file_lock *fl)
 {
 	struct nfs4_delegation *dl = fl->fl_owner;
@@ -4718,11 +4726,11 @@ static bool nfsd_breaker_owns_lease(struct file_lock *fl)
 	struct nfs4_client *clp;
 
 	if (!i_am_nfsd())
-		return NULL;
+		return false;
 	rqst = kthread_data(current);
 	/* Note rq_prog == NFS_ACL_PROGRAM is also possible: */
 	if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
-		return NULL;
+		return false;
 	clp = *(rqst->rq_lease_breaker);
 	return dl->dl_stid.sc_client == clp;
 }