IfAPI: Add capabilities2/capenable2 accessors

[jhibbits]

Summary

As a stopgap measure add basic accessors for the if_capabilities2 and
if_capenable2 members to further hide the ifnet details.

Sponsored by: Juniper Networks, Inc.

[kib]

sys/net/if.c

4277

This seems to be a systematic style(9) bugs.

Also, both 0 and 0xffffffff keep caps intact. Why?

Also, I believe it is reasonable to have a symbolic name like IF_MASK_NONE for the value that keeps the mask(s) intact.

[jhibbits]

sys/net/if.c

4277

The arguments are simply bitmasks, so 'setting' 0 and 'clearing' 0 are nops. I'll remove the conditions, since they really are pointless and this was purely a copy of the if_capabilities accessors. I can add IF_MASK_NONE as 0, but documentation is better in this regard (documentation currently in the works, and will be completed after the IfAPI is fully completed).

[jhibbits]

Address feedback. Clean up the pointless casts.

[kib]

sys/net/if.c

4264

Is this cast to remove const? I think you should use __DECONST then

4325

Is this cast still needed?

4332

Why the cast?

[jhibbits]

sys/net/if.c

4264

Nope, it shouldn't be here. Thought I had cleaned them all up, but looks like I did it in the overall cleanup commit, rather than this one.

[jhibbits]

Address feedback from @kib.

[glebius]

Works for me as a stopgap.