primary_opcode exposed, but no longer used

[n1tehawk]

struct ud still exposes a member field uint8_t primary_opcode;, but decode_opcode() in decode.c no longer assigns to it.

This might potentially break applications relying on the previous behavior (up to and including release 1.7.2) without further notice.

Suggested solution: Either restore the primary_opcode assignment in decode_opcode(), or remove the field completely, so it's usage would generate compiler warnings. I'd prefer the former, as it involves very little overhead and provides information that could be useful.

Regards, NiteHawk

[EDIT] The related commit is 5cd546f.