ANDROID: usb: gadget: u_ether: fix dev->trans_start removal fallout

Upstream commit 9b36627a (net: remove dev->trans_start), removed
dev->trans_start usage in favor of netif_trans_update(). Hence fix the
Android RNDIS multi packet support.

Fixes: AOSP Change-ID: I21c39482718944bb1b1068bdd02f626531e58f08
       ("RNDIS: Add Data aggregation (multi packet) support")
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>