usb: gsi: Fix USB CV L1 suspend test case failure in RNDIS composition

As a part of Remote wakeup test case, in resume path gsi driver
enabling rndis flow control for RNDIS case and starting the
transfers. Followed by L1 test case is running and device sending
NYET for L1 suspend command and failing the test case.

During L1 suspend test case If requests are queued to the Hardware it
will not allow the suspend.

Added is_flow_ctrl_enable flag to ensure whether flow control enabled
by the host with RNDIS_MSG_INIT before. If it is enabled before then only
enable it gain from resume path.

During CV tests host does not send RNDIS_MSG_INT to enable flow control
and test will pass.

Change-Id: Ifd567d910d6571ec3ac0c1eef2da1ee06d9c8fd5
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>
Signed-off-by: Mayank Rana <mrana@codeaurora.org>