kernel: 5.4: import wireguard backport

Rather than using the clunky, old, slower wireguard-linux-compat out of
tree module, this commit does a patch-by-patch backport of upstream's
wireguard to 5.4. This specific backport is in widespread use, being
part of SUSE's enterprise kernel, Oracle's enterprise kernel, Google's
Android kernel, Gentoo's distro kernel, and probably more I've forgotten
about. It's definately the "more proper" way of adding wireguard to a
kernel than the ugly compat.h hell of the wireguard-linux-compat repo.
And most importantly for OpenWRT, it allows using the same module
configuration code for 5.10 as for 5.4, with no need for bifurcation.

These patches are from the backport tree which is maintained in the
open here: https://git.zx2c4.com/wireguard-linux/log/?h=backport-5.4.y
I'll be sending PRs to update this as needed.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
(cherry picked from commit 3888fa7880)
(cherry picked from commit d540725871)
(cherry picked from commit 196f3d586f)
(cherry picked from commit 3500fd7938)
(cherry picked from commit 23b801d3ba)
(cherry picked from commit 0c0cb97da7)
(cherry picked from commit 2a27f6f90a)
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>

target/linux/generic/hack-5.4/260-crypto_test_dependencies.patch

@@ -35,24 +35,6 @@ Signed-off-by: Felix Fietkau <nbd@nbd.name>
  
  config CRYPTO_USER
  	tristate "Userspace cryptographic algorithm configuration"
-@@ -136,8 +136,6 @@ config CRYPTO_USER
- 	  Userspace configuration for cryptographic instantiations such as
- 	  cbc(aes).
- 
--if CRYPTO_MANAGER2
--
- config CRYPTO_MANAGER_DISABLE_TESTS
- 	bool "Disable run-time self tests"
- 	default y
-@@ -145,6 +143,8 @@ config CRYPTO_MANAGER_DISABLE_TESTS
- 	  Disable run-time self tests that normally take place at
- 	  algorithm registration.
- 
-+if CRYPTO_MANAGER2
-+
- config CRYPTO_MANAGER_EXTRA_TESTS
- 	bool "Enable extra run-time crypto self tests"
- 	depends on DEBUG_KERNEL && !CRYPTO_MANAGER_DISABLE_TESTS
 --- a/crypto/algboss.c
 +++ b/crypto/algboss.c
 @@ -240,8 +240,12 @@ static int cryptomgr_schedule_test(struc