rss: Enable portions of RSS globally to enable symmetric hashing

[gallatin]

Summary

We use the fact that all NICs that support hashing are using the
same hash algorithm and hash key to enable symmetic hashing in
TCP, where a software version of the same hash is used to
establish hashes on outgoing connections.

[adrian]

Yup, most multiqueue NICs now just "do" RSS natively whether we want it or not, and the main difference here with RSS defined was whether the configured key or a random key was used, etc.

So exposing the global RSS API for the key management / configuration is fine.

(Eventually I'd like it to be a key we can program in per device and globally, and tweak it all at runtime, but that's later.)

[zlei]

Looks good to me.

[gallatin]

• Made rss_config.c standard. This is needed because most

drivers do not check to see if INET/INET6 is enabled before
setting up RSS. This fixes compilation errors in most
drivers with LINT-NOIP

-Fixed compilattion error with LINT-NOIP after making rss_config
standard. Basically, the net_inet sysctl tree does not exist in
a NOIP kernel. So when in this configuration, hang rss config
off of net instead.