net/dpaa2: revert inner RSS level support

RTE_ETH_RSS_LEVEL_INNERMOST was mapped to the innermost IP instance by
programming the IP key extracts with hdr_index = HDR_INDEX_LAST. The
hardware only resolves that index when several IP headers are stacked.
A non-tunnelled frame carries a single IP header, so the extract
resolves to nothing, the RSS hash is constant and every such frame is
steered to a single Rx queue.

The ethdev API defines INNERMOST by encapsulation level, not by the
presence of a tunnel: a plain frame's innermost header is its only IP
header and must be hashed. The dpaa2 hardware cannot honour that and
keep true inner-only semantics for tunnelled traffic at the same time,
so the level cannot be implemented correctly as merged.

Revert it.
Hashing the outer plus the inner IP under the PMD default level,
which spreads both plain and tunnelled traffic,
should be added in future.

Fixes: 618a06c53d47 ("net/dpaa2: support inner RSS level for tunnel")

Signed-off-by: Maxime Leroy <maxime@leroys.fr>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>