ipfw: Update the pfil mbuf pointer in ipfw_check_frame()

[markj]

Summary

ipfw_chk() might call m_pullup() and thus can change the mbuf chain
head. In this case, the new chain head has to be returned to the pfil
hook caller.

PR: 256439
Fixes: f355cb3e6
MFC after: 3 days

[ae]

I think we can set *p.m unconditionally, like we do in ipfw_check_packet().

[markj]

In D30764#691796, @ae wrote:

I think we can set *p.m unconditionally, like we do in ipfw_check_packet().

p is a union of struct mbuf ** and void *. So wouldn't setting *p.m do the wrong thing if the packet is passed with PFIL_MEMPTR?

[ae]

In D30764#691856, @markj wrote:

p is a union of struct mbuf ** and void *. So wouldn't setting *p.m do the wrong thing if the packet is passed with PFIL_MEMPTR?

You are right.