tc: fq: add support for JSON output

tc: fq: add support for JSON output

Enable proper JSON output for the FQ Qdisc.
Use the "KEY VALUE" format for oneline output of statistics instead of
"VALUE KEY", and remove unnecessary commas from the output.
Use sprint_size() to print size values in fq_print_opt().
Use sprint_time64() to print time values in fq_print_xstats().
Also, update the man page to reflect the changes in the output format.

Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Leslie Monis <lesliemonis@gmail.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>