netlink: do not enter direct reclaim from netlink_trim()

In commit d35c99ff ("netlink: do not enter direct reclaim from
netlink_dump()") we made sure to not trigger expensive memory reclaim.

Problem is that a bit later, netlink_trim() might be called and
trigger memory reclaim.

netlink_trim() should be best effort, and really as fast as possible.
Under memory pressure, it is fine to not trim this skb.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -1210,7 +1210,9 @@ static struct sk_buff *netlink_trim(struct sk_buff *skb, gfp_t allocation)
 		skb = nskb;
 	}
 
-	if (!pskb_expand_head(skb, 0, -delta, allocation))
+	if (!pskb_expand_head(skb, 0, -delta,
+			      (allocation & ~__GFP_DIRECT_RECLAIM) |
+			      __GFP_NOWARN | __GFP_NORETRY))
 		skb->truesize -= delta;
 
 	return skb;