https://github.com/solana-labs/solana/pull/16646
removed first_coding_index since the field is currently redundant and
always equal to fec_set_index.
However, with upcoming changes to erasure coding schema, this will no
longer be the same as fec_set_index and so requires a separate field to
represent.
(cherry picked from commit 49ba09b333
)
Co-authored-by: behzad nouri <behzadnouri@gmail.com>