Zephyr's MQTT does not implement a client's message queue.
So, a race-condition may be present when multiple messages are
received and processed.
We remove the pinreq function call to allow the mqtt_read function
to handle all the incoming messages.
CONFIG_IP_BUF_RX_SIZE is also updated to allow more messages to be
queued by the IP stack.
Jira: ZEP-669
Change-Id: Ie3ef55b17020e04c6540adf975a66fb004933914
Signed-off-by: Flavio Santes <flavio.santes@intel.com>
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