svcrpc: ensure gss DESTROY tokens free contexts from cache

If we don't do this then we'll end up with a pointless unusable context
sitting in the cache until the time the original context would have
expired.
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>

net/sunrpc/auth_gss/svcauth_gss.c

@@ -1126,6 +1126,7 @@ svcauth_gss_accept(struct svc_rqst *rqstp, __be32 *authp)
 	case RPC_GSS_PROC_DESTROY:
 		if (gss_write_verf(rqstp, rsci->mechctx, gc->gc_seq))
 			goto auth_err;
+		rsci->h.expiry_time = get_seconds();
 		set_bit(CACHE_NEGATIVE, &rsci->h.flags);
 		if (resv->iov_len + 4 > PAGE_SIZE)
 			goto drop;