fix a bug that leads to a crash when binat rules of the form 'binat from ... to ... -> (if)' are used, where the interface is dynamic.
fix a bug that leads to a crash when binat rules of the form
'binat from ... to ... -> (if)' are used, where the interface
is dynamic.

Discovered by:	kos(at)bastard(dot)net
Analyzed by:	Pyun YongHyeon
Approved by:	mlaier (mentor)
MFC after:	1 week

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