wireguard: allowedips: initialize list head in selftest

The randomized trie tests weren't initializing the dummy peer list head,
resulting in a NULL pointer dereference when used. Fix this by
initializing it in the randomized trie test, just like we do for the
static unit test.

While we're at it, all of the other strings like this have the word
"self-test", so add it to the missing place here.

Fixes: e7096c13

 ("net: WireGuard secure network tunnel")
Cc: stable@vger.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>