We accept either the first offer received, or an offer for the

We accept either the first offer received, or an offer for the
current address if one arrives inside select_timeout. So there
is no need to keep a list of received offers. Just keep the
best one and DECLINE the rest. Nuke now unused 'offered_leases'
TAILQ.

Also fixes the oddity that the *last* offer for the current
address is taken rather than the *first*.