wireguard: queueing: use CFI-safe ptr_ring cleanup function

wireguard: queueing: use CFI-safe ptr_ring cleanup function

We make too nuanced use of ptr_ring to entirely move to the skb_array
wrappers, but we at least should avoid the naughty function pointer cast
when cleaning up skbs. Otherwise RAP/CFI will honk at us. This patch
uses the __skb_array_destroy_skb wrapper for the cleanup, rather than
directly providing kfree_skb, which is what other drivers in the same
situation do too.

Reported-by: PaX Team <pageexec@freemail.hu>
Fixes: c1c9ed76571c ("wireguard: receive: use ring buffer for incoming handshakes")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>