Filter: trying to drop the sparse two-byte instruction code

  F(clist_add_del,	'C', 'a') \

  F(roa_check,		'R', 'C')

enum filter_instruction_code {

  fi_invalid = 0,

#define F(c,a,b) fi_##c,

FI_LIST

#undef F

};

/*

enum filter_instruction_code {

#define F(c,a,b) \

  fi_##c = FI_TWOCHAR(a,b),

FI_LIST

#undef F

};

*/

struct f_inst {		/* Instruction */

  struct f_inst *next;	/* Structure is 16 bytes, anyway */