Merge branch 'tun-allow-to-attach-eBPF-filter'

Jason Wang says:

====================
tun: allow to attach eBPF filter

This series tries to implement eBPF socket filter for tun. This could
be used for implementing efficient virtio-net receive filter for
vhost-net.

Changes from V2:
- fix typo
- remove unnecessary double check
====================

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