mwifiex: fix soft lockup during iperf UDP RX

A soft lockup was observed on ARM multicore platform while UDP
RX iperf was running on station.

Reason for this is delay_main_task was not taken into consideration while
jumping to process_start. Now if delay_main_task is true, we would exit
mwifiex_main_process instead of going to process_start again.
This ensure other process is scheduled on this CPU and soft lockup is avoided.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kevin Gan <ganhy@marvell.com>
Signed-off-by: Marc Yang <yangyang@marvell.com>
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>