igc: make the hardware RSS hash agree with the stack's configuration

[rcm]

Summary

rss_gethashconfig() is available without options RSS since d9c55b2e8cd6.
Use it to program MRQC, as ixl(4), ice(4) and iavf(4) do, instead of a
fixed field set that included UDP 4-tuple, which the configuration
excludes unless net.inet.rss.udp_4tuple is set. UDP is now hashed on
addresses only by default.

Also report the UDP hash types on receive; they were passed up as
M_HASHTYPE_NONE.

Fixes: 517904de5cca ("igc(4): Introduce new driver for the Intel I225 Ethernet controller.")
Sponsored by: Rubicon Communications, LLC ("Netgate")

Test Plan

Tested on an I225-LM with four queues forwarding a UDP flood: UDP
packets now arrive with M_HASHTYPE_RSS_IPV4 (RSS_UDP_IPV4 with
udp_4tuple), rss_mbuf_software_hash_v4() accepts the hash, and netisr
handles each packet on the CPU of the queue it arrived on; before,
nearly every UDP packet was rehashed and queued to another CPU.

[kbowling]

I thought the idea of d9c55b2e8cd6b79f6926278e10a79f1bcca27a4b was to get rid of most of the ifdef. rss_gethashconfig is a public function, why not just apply what you have in the ifdef RSS section always?

[rcm]

In D60284#1383431, @kbowling wrote:

I thought the idea of d9c55b2e8cd6b79f6926278e10a79f1bcca27a4b was to get rid of most of the ifdef. rss_gethashconfig is a public function, why not just apply what you have in the ifdef RSS section always?

Ah yes thanks for pointing that out, I have updated the diff accordingly

[rcm]

add full-context diff. no other changes.

[kbowling]

Looks good to me. There are probably similar elsewhere in the tree.