net: usbnet: Fix nanosec timestamp print in IPC log

Currently the IPC log statement uses %lu format specifier to
print the nanosec timestamp. Since this value will circularly
loop from 000000000 to 999999999, there might be a case of
incorrect info being dumped onto the IPC log. For example, if the
actual time value is 987.012345678, the IPC log would show
987.12345678 instead.
Fix this by using %09lu format specifier for nanosec timestamp so
as to preserve leading zeros.

Change-Id: I7e962f4a1f7981f48c72d0cc55e41995e9dfb195
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>