octeontx2-af: fix LD CUSTOM LTYPE aliasing

Since LD contains LTYPE definitions tweaked toward efficient
NIX_AF_RX_FLOW_KEY_ALG(0..31)_FIELD(0..4) usage, the original location
of NPC_LT_LD_CUSTOM0/1 was aliased with MPLS_IN_* definitions.
Moving custom frame to value 6 and 7 removes the aliasing at the cost of
custom frames being also considered when TCP/UDP RSS algo is configured.

However since the goal of CUSTOM frames is to classify them to a
separate set of RQs, this cost is acceptable.

Signed-off-by: Stanislaw Kardach <skardach@marvell.com>
Acked-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>