Added DATA opcode support to ApfGenerator This commit adds support for the "DATA" opcode to ApfGenerator. This opcode add data section to the beginning of the program which can be used to construct the offload packet later. * design doc: go/apf-v6-proposal Bug: 293811969 Test: TH Change-Id: I3c05538b7454259d8a80911b075c811ea7403d67