net: usbnet: Add UTC timestamp logging for packets

Add UTC timestamp logs in usbnet class driver for incoming and
outgoing data packets. This is required for packet profiling,
latency calculations and debug purposes.

By default, the skb and urb kernel addresses will show up as 0's.
To expose actual addresses, please run the command:
 echo 0 > /proc/sys/kernel/kptr_restrict

Change-Id: I3cf54eb5d38498c7858b0db07c37c0eaf93c8c37
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>