qlnx: Derive the hardware RSS key from the common key

[kbowling]

Summary

Replace the embedded default key with rss_getkey().  Decode each group
of four key bytes as a big-endian word; the shared code then serializes
those host-order words as little-endian firmware fields.  This preserves
the existing hardware representation for the common default and allows
a configured common key to take effect.

Keep the existing multi-queue gate, RSS hash selections, and indirection
policy unchanged.

MFC after:      2 weeks
Sponsored by:   BBOX.io