bloom: fix logic controlling bloom regeneration

bloom: fix logic controlling bloom regeneration

Add missing MAX_BLOOM_BITS index in the logic in bup bloom that
determines whether or not we should regenerate the filter.  We never
noticed because:

  $ python2
  >>> 0 < {1 : 2}
  True

  $ python3
  >>> 0 < {1 : 2}
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  TypeError: '<' not supported between instances of 'int' and 'dict'

Also regnerate if the -k value differs from the existing filter's k.

Thanks to Johannes Berg for pointing out some nontrivial problems in
an earlier version.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>