pipeline: rework optimization pattern for header generation

pipeline: rework optimization pattern for header generation

The P4 language requires marking a header as valid before any of the
header fields are written as opposed to after the writes are done.
Hence, the optimization of replacing the sequence of instructions to
generate a header by reading it from the table action data with a
single DMA internal instruction are reworked from "mov all + validate
-> dma" to "validate + mov all -> dma".

Signed-off-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>