MINOR: listener: move LI_O_UNLIMITED and LI_O_NOSTOP to bind_conf

MINOR: listener: move LI_O_UNLIMITED and LI_O_NOSTOP to bind_conf

These two flags are entirely for internal use and are even per proxy
in practice since they're used for peers and CLI to indicate (for the
first one) that the listener(s) are not subject to connection limits,
and for the second that the listener(s) should not be stopped on
soft-stop. No need to keep them in the listeners, let's move them to
the bind_conf under names BC_O_UNLIMITED and BC_O_NOSTOP.