net: Make check_next_chunk() mutually exclusive

net: Make check_next_chunk() mutually exclusive

Since 4004285311 ("Fix the race in data_finished() and resp_finished()"),
Although the possibility of a race between two threads executing
data_finished() and resp_finished() is reduced, it is still possible
to enter the check_next_chunk() function at the same time in certain
circumstances as below:

		Thread A			 |			Thread B
-------------------------------------------------+--------------------------------------------------------------
						 |	chunk->resp_finished = 1;
chunk->data_finished = 1;			 |
if (chunk->resp_finished)	   		 |
	check_next_chunk(chunk, transfer);	 |
chunk->chunk_number = transfer->chunk_number++;  |
						 |	if (chunk->data_finished)
						 |		check_next_chunk(chunk, transfer);
						 |	     >> chunk->chunk_number = transfer->chunk_number++;
                                                 |		<chunk_number becomes unmatched>
chunk->data_finished = chunk->resp_finished = 0; |
…

To address this, this makes the functions completely mutually exclusive.

Change-Id: I94df217ec82dadc322050693e86763f9c8213d05
Signed-off-by: Dongwoo Lee <dwoo08.lee@samsung.com>