xC-gen-proto: reduce enums to single bytes

That's already way more than we can possibly use.

xC-gen-proto-c.awk

@@ -110,11 +110,11 @@ function codegen_enum(name, cg,    ctype) {
 
 	# XXX: This should also check if it isn't out-of-range for any reason,
 	# but our usage of sprintf() stands in the way a bit.
-	CodegenSerialize[name] = "\tstr_pack_i32(w, %s);\n"
+	CodegenSerialize[name] = "\tstr_pack_i8(w, %s);\n"
 	CodegenDeserialize[name] = \
 		"\t{\n" \
-		"\t\tint32_t v = 0;\n" \
-		"\t\tif (!msg_unpacker_i32(r, &v) || !v)\n" \
+		"\t\tint8_t v = 0;\n" \
+		"\t\tif (!msg_unpacker_i8(r, &v) || !v)\n" \
 		"\t\t\treturn false;\n" \
 		"\t\t%s = v;\n" \
 		"\t}\n"