tc: fix second printing of requeues

tc: fix second printing of requeues

Non-JSON tc qdisc output used to print the "requeues" statistic
twice.  Commit 4fcec7f3665b ("tc: jsonify stats2") tried to preserve
this behaviour for both standard output and JSON, but used the wrong
statistic (q.qlen).  Also duplicating keys in JSON is not allowed,
so the second occurrence should be completely skipped with JSON.

Fixes: 4fcec7f3665b ("tc: jsonify stats2")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>