usb: mdm_bridge: Make rx_done queue length check independent of rx throttle

rx_done queue length was checked only when rx throttle condition was true.
rx throttle condition is asynchronous because of which sometimes queue
length value becomes much larger than stop_submit_urb_limit when rx
throttled condition is false. Hence check the queue length irrespective of
the rx throttle condition before submitting the rx urb. Also increase the
stop_submit_urb_limit to same as the flow control enable threshold value
in downlink direction.

Change-Id: I3dd915b04bfe7640a98e40809831a7b45c39dfd7
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>