kernel: copy kernel 4.19 code to 5.4

No changes were done to the patches while coping them. Currently they do
not apply on top of kernel 5.4.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/generic/pending-5.4/616-net_optimize_xfrm_calls.patch

@@ -0,0 +1,20 @@
+From: Felix Fietkau <nbd@nbd.name>
+Subject: kernel: add a small xfrm related performance optimization
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+ net/netfilter/nf_nat_core.c | 3 +++
+ 1 file changed, 3 insertions(+)
+
+--- a/net/netfilter/nf_nat_core.c
++++ b/net/netfilter/nf_nat_core.c
+@@ -110,6 +110,9 @@ int nf_xfrm_me_harder(struct net *net, s
+ 	struct sock *sk = skb->sk;
+ 	int err;
+ 
++	if (skb->dev && !dev_net(skb->dev)->xfrm.policy_count[XFRM_POLICY_OUT])
++		return 0;
++
+ 	err = xfrm_decode_session(skb, &fl, family);
+ 	if (err < 0)
+ 		return err;