address lists, at_ifaddr_list. Acquire the lock, and use ifaddr
refcounts where necessary, to close most known address-related
races in netatalk.
Annotate one potential race in at_control() where we acquire an
ifaddr reference, drop the global lock, and scrub the address from
the ifnet before re-acquiring the global lock, which could allow
for a writer-writer race.
MFC after: 3 weeks
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