We used to regenerate our descriptor whenever we'd get a sighup. This
was caused by a bug in options_transition_affects_workers() that would
return true even if the options were exactly the same. Down the call
path we'd call init_keys(), which made us make a new descriptor which
the authorities would reject, and the node would subsequently fall out
of the consensus.

This patch fixes only the first part of this bug:
options_transition_affects_workers() behaves correctly now. The second
part still wants a fix.