This PR makes the modem_pipe instances track if they have
data ready to receive, and invoke the RECEIVE_READY event
every time they are attached if the backend implementing
the pipe has notified that receive is ready.
This mechanism ensures that modules attaching to a pipe
get the async RECEIVE_READY event immediately after
attaching to a pipe if there is data ready, instead of
having to poll the pipe, or worse, wait until newer data
becomes available.
The addition revealed a timing issue in the cmux test
suite. Specifically the CMUX instance now immediately
receives the response to a command which the CMUX
instance has not sent yet, causing it to drop the
response.
The CMUX test suite now uses the transaction
mechanism of the mock_pipe to wait for the command
before sending the response.
Signed-off-by: Bjarki Arge Andreasen <bjarkix123@gmail.com>
40b9f51ee5