Merge branch 's390-bpf-push-pop'

Michael Holzheu says:

====================
s390/bpf: recache skb->data/hlen for skb_vlan_push/pop

Here the s390 backend for Alexei's patch 4e10df9a60d9 ("bpf: introduce
bpf_skb_vlan_push/pop() helpers") plus two bugfixes and two minor
improvements.

The first patch "s390/bpf: clear correct BPF accumulator register" will
also go upstream via Martin's "fixes" branch.

* v2: Integrated suggestions from Joe Perches
====================

Signed-off-by: David S. Miller <davem@davemloft.net>