AdvSendAdvert checked in send.c only

This setting way being check in send_ra and in the places where send_ra
was called.  There's no need to check it twice and to duplicate less
code may as well check it right in send_ra.

Also in this change, return -1 when send_ra fails.
removing ensure_iface_setup

ensure_iface_setup was called from send_ra.  The responsibility of setting
up ifaces is not in the send function.  If an interface is not setup, it
should not be scheduled and netlink should set it up when the kernel says
the interface is ready.  However, I suppose if we somehow get a solicit on
the interface and the interface is not ready, we should attempt to make it
ready at that point.
handle if/when we get an rs on a not ready iface

There is a chance that we could get an rs on an interface which
is not ready (for example, when netlink processing can't keep up).
I'm not sure if this is realistic, but if it ever happens, attempt
to handle it properly.