agbindrec: realign parameter names in prototype with definition

agbindrec: realign parameter names in prototype with definition

The C compiler does not care if these names mismatch, but it is less confusing
to be consistent. This change leaves the obj/arg_obj discrepancy alone under the
justification that "arg_obj" is not any more useful externally-facing and "obj"
internally would conflict with an already existing local.