nfp: rename ring allocation helpers

"Shadow" in ring helpers used to mean that the helper will allocate
rings without touching existing configuration, this was used for
reconfiguration while the device was running.  We will soon use
the same helpers for .ndo_open() path, so replace "shadow" with
"ring_set".

No functional changes.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>