There is an m_pullup() down in AH input. As it may free or change

There is an m_pullup() down in AH input.  As it may free or change
the mbuf, the callers must be careful.  Although there is no bug,
use the common pattern to handle this.  Pass down an mbuf pointer
mp and let m_pullup() update the pointer in all callers.
It looks like the tcp signature functions should not be called.
Avoid an mbuf leak and return an error.
OK mvs@