vnic nicvf: Program the common RSS key in network word order

[kbowling]

Summary

Replace the repeated hardware-reset key with rss_getkey().  Decode each
eight-byte chunk with be64dec() into the register-word array before
programming the five key registers.

This matches the key serialization in DPDK's nicvf_rss_set_key(), added
by commit 7694fab264ac666d62a4cae04f2979991ce64259
("net/thunderx/base: add RSS and RETA configuration").  A raw copy into
the word array on little-endian hosts would reverse bytes within each
register relative to that convention.

Preserve the CPI-algorithm gate, enabled hash fields, and round-robin
indirection table.