nfp: bpf: rename ALU_OP_NEG to ALU_OP_NOT

The current ALU_OP_NEG is Op encoding 0x4 for NPF ALU instruction. It is
actually performing "~B" operation which is bitwise NOT.

The using naming ALU_OP_NEG is misleading as NEG is -B which is not the
same as ~B.

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