mon: relax feature bit requirements for peer mons

Instead of requiring that peer mons have *exactly* the same set of
features, relax this somewhat for features that we know don't matter.
For starters, the OSD_SET_ALLOC_HINT does not affect the mon (or overlap
with a mon behavior change that does matter).

Fixes: #10178
Backport: giant
Signed-off-by: Sage Weil <sage@redhat.com>