pf: Save the protocol number in the pf_fragment

[kp]

Summary

When we try to look up a pf_fragment with pf_find_fragment() we compare (see
pf_frag_compare()) addresses (and family), id but also protocol.
We failed to save the protocol to the pf_fragment in pf_fragcache(), resulting
in failing reassembly.

[philip]

Are you sure that's all of the fields in (*frag) now? :-)

Approved by: philip (mentor)

[kp]

Yes. We need to get all of the fields used in pf_frag_compare(). That's fr_id, fr_proto, fr_af, fr_src and fr_dst.