- Update to version 0.0.20180420
== Changes ==
* wg-quick: account for specified fwmark in auto routing mode

If we're doing automatic routing with default routes, but the config has
also specified an explicit fwmark, then use that explicit fwmark, even
if it's conflicting, since the administrator has explicitly opted into
using it. Also, when shutting down the interface, we only now remove the
fancy rules if we're in automatic routing mode with default routes.

* send: account for route-based MTU

It might be that a particular route has a different MTU than the
interface, via `ip route add ... dev wg0 mtu 1281`, for example. In this
case, it's important that we don't accidently pad beyond the end of the
MTU. We accomplish that in this patch by carrying forward the MTU from
the dst if it exists. We also add a unit test for this issue.

* send: simplify skb_padding with nice macro
* blake2s: remove unused helper
* compat: remove unused dev_recursion_level backport

Cleanups.

* poly1305: do not place constants in different sections

We're referencing these constants as one contiguous blob, so if there's
any merging that goes on with other constants elsewhere (such as the
kernel's current poly1305 implementation that we hope to replace), then
these will be reordered and have the wrong values.