f_gsi: Send DTR status with GET_LINE_STATE ioctl for RMNET interface

If there is any pending TRB on IN/INT endpoint with USB device
controller, USB device controller doesn't go into USB host requested
L1 LPM. If USB RMNET GSI driver gets modem offline command or any
control data from modem through user space application while running
USB L1 suspend/resume compliance test case, this compliance test case
fails due to pending TRB. Currently driver is using connected flag
related value as line state instead of actual DTR status i.e. USB host
side RMNET driver state. This allows QTI application to write available
control packet notification towards host whereas host side driver is
not ready to perform I/O. Hence to fix this issue use actual DTR status
with GET_LINE_STATE ioctl for RMNET interface.

Change-Id: Ib2ed004407a8b9336cbbe42b3735750946e6c759
Signed-off-by: Mayank Rana <mrana@codeaurora.org>