USB: u_bam_data: Call msm_ep_unconfig() in stop_rndis_ipa()

Host rndis driver sends control request to enable/disable flow control
on device side as part of driver unstal/install. This flow control
calls stop/start rndis_ipa which results in disconnect_work/connect_work
being executed. As part of stop rndis_ipa(), it needs to call
msm_ep_unconfig() to change ep file operations, otherwise DBM endpoint
configuration will not happen when start rndis_ipa() is called. This might
lead to NOC error or ip address not assigned after new driver installation.
Fix this by calling msm_ep_unconfig() during stop rndis_ipa().

Change-Id: I86e0a49075d84d727c028568b931bf5a3649c13a
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>