ifnet: use ck_pr(3) store & load setting ifnet pointer in ifindex

[glebius]

Summary

The lockless access to the array is protected by the network epoch.

[bz]

I think there should only be one function for "store" pointer which is ifnet_setbyindex(); that'll be possible if you consider my comment from D33259; though in the longer term it probably won't matter to have the other one for ifindex_free() as we'd still guarantee that all accesses go through wrapper functions so we can keep changing the internals.

If you can explain the added WASSERT I am fine with this.

sys/net/if.c

416

Contrary to your description, why do you need to add this suddenly here?

[glebius]

sys/net/if.c

416

Can be removed, but it still removed when all index allocation bits are merged into one in D33262