Reduce stack usage by 256 bytes per call. It helps to avoid kernel stack overflow in complicated traffic filtering setups.
Reduce stack usage by 256 bytes per call. It helps to avoid kernel
stack overflow in complicated traffic filtering setups.

There can be minor performance degradation for the MHLEN < len <= 256 case
due to additional buffer allocation, but it is a rare case.

Approved by:	re (rwatson), glebius (mentor)
MFC after:	1 week

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