wireguard: bump to 1.0.20200429

wireguard: bump to 1.0.20200429

* compat: support latest suse 15.1 and 15.2
* compat: support RHEL 7.8's faulty siphash backport
* compat: error out if bc is missing
* compat: backport hsiphash_1u32 for tests

We now have improved support for RHEL 7.8, SUSE 15.[12], and Ubuntu 16.04.

* compat: include sch_generic.h header for skb_reset_tc

A fix for a compiler error on kernels with weird configs.

* compat: import latest fixes for ptr_ring
* compat: don't assume READ_ONCE barriers on old kernels
* compat: kvmalloc_array is not required anyway

ptr_ring.h from upstream was imported, with compat modifications, to our
compat layer, to receive the latest fixes.

* compat: prefix icmp[v6]_ndo_send with __compat

Some distros that backported icmp[v6]_ndo_send still try to build the compat
module in some corner case circumstances, resulting in errors.  Work around
this with the usual __compat games.

* compat: ip6_dst_lookup_flow was backported to 3.16.83
* compat: ip6_dst_lookup_flow was backported to 4.19.119

Greg and Ben backported the ip6_dst_lookup_flow patches to stable kernels,
causing breaking in our compat module, which these changes fix.

* git: add gitattributes so tarball doesn't have gitignore files

Distros won't need to clean this up manually now.

* crypto: do not export symbols

These don't do anything and only increased file size.

* queueing: cleanup ptr_ring in error path of packet_queue_init

Sultan Alsawaf reported a memory leak on an error path.

* main: mark as in-tree

Now that we're upstream, there's no need to set the taint flag.

* receive: use tunnel helpers for decapsulating ECN markings

ECN markings are now decapsulated using RFC6040 instead of the old RFC3168.

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