drbd: Use struct_group() to zero algs

drbd: Use struct_group() to zero algs

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add a struct_group() for the algs so that memset() can correctly reason
about the size.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20211118203712.1288866-1-keescook@chromium.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>