Revert "wireguard: use DEV_STATS_INC()"

This reverts commit be41c0c4 which is
commit 93da8d75 upstream.

It breaks the build due to other patches being reverted for Android abi
issues.  If it needs to come back in the future, it can in an abi-safe
way.

Bug: 161946584
Change-Id: I2f03cb599bb1c60390aa405159cb19dc3406c84d
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>