usb: mdm_bridge: Increase the number of rx urbs

Due to higher HSIC interrupt threshold value, sometimes
driver is running short of enough rx urbs queued to HSIC
HW to receive IP packets from mdm device. In this case
driver is busy processing large number of completed rx
urbs and left with fewer pending urbs with HW. This causes
occasional throughput drops on rx data path. Hence increase
number of rx urb from 50 to 100, to keep HSIC HW busy in
pulling data from mdm device while completed urbs are getting
processed.

CRs-Fixed: 397809
Change-Id: Ibe067d08de02d3601ea5948a20b01098d57d1dd3
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>