Fix the race in data_finished() and resp_finished()

Fix the race in data_finished() and resp_finished()

Setting the data_finished and resp_finished flags too early sometimes
led to a situation in which another chunk was sent, even though the
functions had not finished executing, which resulted in a flashing
error.

For example:
When data_finished() was called, the flag data_finished was set. Then
after entering aio_error/aio_return the thread would be put to sleep and
the program would start executing the resp_finished() function. The
function was executed to the end and because data_finished flag was set,
the check_next_chunk() was called.
After that, the thread with data_finished() would return from sleep and
continue its execution, even though the data it was pointing to at that
moment is out of date. This led, among other things, to a mismatch
between numbers of chunk and the response.

Change-Id: I404b3723cb9e671d13221bff2b7823f1fdc43906
Signed-off-by: Mateusz Moscicki <m.moscicki2@samsung.com>
(cherry picked from commit 400428531184493e9d025af29286d071f84c1115)