ipc: freebsd: move if_wg path to reflect new in-tree location

ipc: freebsd: move if_wg path to reflect new in-tree location

When we re-added if_wg to the tree, we changed directories in dev to
strip the if_ (we don't use this prefix for other interfaces'
directories). Adjust it here as a convenience, so that when we import
wireguard-tools to FreeBSD the path will just work as-is with our usual
build.

Signed-off-by: Kyle Evans <kevans@FreeBSD.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>