usb: gadget: f_ncm: Revert to upstream

Revert the following changes to restore to upstream version:

commit ff25c3b1 ("usb: gadget: f_ncm: allocate/free net device upon driver bind/unbind")
commit fbbccfe9 ("usb: gadget: Add check gadget function bind or not")

Reason for revert: Causes gether_set_ifname() support to kernel panic.

Change-Id: I51064467cad63e47a4a9734f18f1a5b95fa8db86