usb: rndis: allow for cable disconnect in RNDIS

The change cancels the setting of ipa_supported to false
on cable disconnect. ipa_supported should only change its
setting during composition changes - i.e. bind and unbind

Change-Id: I5ad1ff560c51d46276cbc50e9c584ee72314b920
Signed-off-by: Dov Levenglick <dovl@codeaurora.org>