wireguard: bump to 0.0.20190406

wireguard: bump to 0.0.20190406

* allowedips: initialize list head when removing intermediate nodes

Fix for an important regression in removing allowed IPs from the last
snapshot. We have new test cases to catch these in the future as well.

* tools: warn if an AllowedIP has a nonzero host part

If you try to run `wg set wg0 peer ... allowed-ips 192.168.1.82/24`, wg(8)
will now print a warning. Even though we mask this automatically down to
192.168.1.0/24, usually when people specify it like this, it's a mistake.

* wg-quick: add 'strip' subcommand

The new strip subcommand prints the config file to stdout after stripping
it of all wg-quick-specific options. This enables tricks such as:
`wg addconf $DEV <(wg-quick strip $DEV)`.

* tools: avoid unneccessary next_peer assignments in sort_peers()

Small C optimization the compiler was probably already doing.

* peerlookup: rename from hashtables
* allowedips: do not use __always_inline
* device: use skb accessor functions where possible

Suggested tweaks from Dave Miller.

* blake2s: simplify
* blake2s: remove outlen parameter from final

The blake2s implementation has been simplified, since we don't use any of the
fancy tree hashing parameters or the like. We also no longer separate the
output length at initialization time from the output length at finalization
time.

* global: the _bh variety of rcu helpers have been unified
* compat: nf_nat_core.h was removed upstream
* compat: backport skb_mark_not_on_list

The usual assortment of compat fixes for Linux 5.1.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>