v0 protocol: use size_t for capability length/offset

When parsing server capabilities, we use "int" to store lengths and
offsets. At first glance this seems like a spot where our parser may be
confused by integer overflow if somebody sent us a malicious response.

In practice these strings are all bounded by the 64k limit of a
pkt-line, so using "int" is OK. However, it makes the code simpler to
audit if they just use size_t everywhere. Note that because we take
these parameters as pointers, this also forces many callers to update
their declared types.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

upload-pack.c

@@ -1067,7 +1067,7 @@ static void receive_needs(struct upload_pack_data *data,
 		const char *features;
 		struct object_id oid_buf;
 		const char *arg;
-		int feature_len;
+		size_t feature_len;
 
 		reset_timeout(data->timeout);
 		if (packet_reader_read(reader) != PACKET_READ_NORMAL)