IfAPI: Add l2com accessor for firewire.

[jhibbits]

Summary

There may be a better spot for this, since it's *only* used for
Firewire, all other accesses of ifp->if_l2com are handled within the
netstack.

Sponsored by: Juniper Networks, Inc.

[melifaro]

sys/net/if.c

4944

Maybe it's worth returning struct fw_com * so we don't need an explicit typecast afterwards?

[jhibbits]

sys/net/if.c

4944

It would need to be a more specific name then, because if_l2com is general L2 private data used elsewhere directly by the netstack. Firewire is using it for its own L2 bits.

[melifaro]

sys/net/if.c

4944

Makes sense. Anyway, It'll probably be entirely eliminated in 15, so I guess it doesn't matter much.

[glebius]

In the original BSD stack if_l2com was used by multiple subsystems. Today firewire is the very last user of if_register_com_alloc() and thus of if_com_alloc[] array. The ng_ether(4) is the second last user of if_l2com field itself. Given that firewire is already an obsoleted driver, I don't see a good reason to provide official API to access this field. But if the API as marked as destined to be removed soon, I don't mind.

[glebius]

I'm working on a patch that would remove if_l2com use from firewire. However, I have nothing to test it on. My last firewire was 3 mainboards ago :)

[glebius]

Please commit whatever version that fits your work, on the second thought I don't think it is worth investing much time in firewire.