Also tweak the allocator to be more aggressive about keeping it full.
The recent changes to make updates to interior nodes transactional (and
thus generate updates to the alloc btree) all put more stress on the
btree node reserves.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>