Check that the interface is on the list of cloned interfaces before trying to remove it to avoid panics in case of two threads trying to remove it in parallel.
Check that the interface is on the list of cloned interfaces before trying
to remove it to avoid panics in case of two threads trying to remove it in
parallel.

PR:		kern/116837
Submitted by:	Takahiro Kurosawa (takahiro.kurosawa gmail.com) (orig version)
MFC after:	10 days

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