net: hamradio: baycom_ser_fdx: Replace timeval with timespec64

32 bit systems using 'struct timeval' will break in the year 2038, so
we replace the code appropriately. However, this driver is not broken
in 2038 since we are only using microseconds portion of the time.

This patch replaces 'struct timeval' with 'struct timespec64'. We only
need to find elapsed microseconds rather than absolute time, so it's
better to use monotonic time, so using ktime_get_ts64() makes the code
more efficient and more robust against concurrent settimeofday()
calls.

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Thomas Sailer <t.sailer@alumni.ethz.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>