parse-options.h: use consistent name for the callback parameters
In the various OPT_* macros the 'f' parameter is usually used to
specify flags, while the 'cb' parameter is used to specify a callback
function. OPT_CALLBACK and OPT_NUMBER_CALLBACKS, however, are
inconsistent with the rest, as they use 'f' to specify their callback
function.
Rename their callback macro parameters to 'cb' to avoid the
inconsistency.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>