Merge branch 'bpf-fix-xsk-wakeup'

Merge branch 'bpf-fix-xsk-wakeup'

Maxim Mikityanskiy says:

====================
This series addresses the issue described in the commit message of the
first patch: lack of synchronization between XSK wakeup and destroying
the resources used by XSK wakeup. The idea is similar to napi_synchronize.
The series contains fixes for the drivers that implement XSK.

v2 incorporates changes suggested by Björn:

1. Call synchronize_rcu in Intel drivers only if the XDP program is
   being unloaded.
2. Don't forget rcu_read_lock when wakeup is called from xsk_poll.
3. Use xs->zc as the condition to call ndo_xsk_wakeup.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>