iw: Print TXQ statistics for stations and interfaces

iw: Print TXQ statistics for stations and interfaces

This adds printing of TXQ statistics for stations and interfaces when
supplied by the kernel. For stations, another section is added when verbose
mode is enabled; for interfaces, the multicast queue information is always
printed when available.

This is the information also available through debugfs in
/sys/kernel/debug/ieee80211/phyX/netdev:Y/aqm and
/sys/kernel/debug/ieee80211/phyX/netdev:Y/stations/*/aqm.

Sample output:

$ iw dev wlp2s0 station dump -v
Station xx:xx:xx:xx:xx:xx (on wlp2s0)
[...]
	TXQs:
		TID	qsz-byt	qsz-pkt	flows	drops	marks	overlmt	hashcol	tx-bytes	tx-packets
		0	0	0	0	0	0	0	0	0		0
		1	0	0	0	0	0	0	0	0		0
		2	0	0	0	0	0	0	0	0		0
		3	0	0	0	0	0	0	0	0		0
		4	0	0	0	0	0	0	0	0		0
		5	0	0	0	0	0	0	0	0		0
		6	0	0	0	0	0	0	0	0		0
		7	0	0	0	0	0	0	0	0		0
		8	0	0	0	0	0	0	0	0		0
		9	0	0	0	0	0	0	0	0		0
		10	0	0	0	0	0	0	0	0		0
		11	0	0	0	0	0	0	0	0		0
		12	0	0	0	0	0	0	0	0		0
		13	0	0	0	0	0	0	0	0		0
		14	0	0	0	0	0	0	0	0		0
		15	0	0	0	0	0	0	0	0		0
[...]

$ iw dev wlp2s0 info
Interface wlp2s0
	ifindex 9
	wdev 0x1
	addr xx:xx:xx:xx:xx:xx
	type AP
	wiphy 0
	channel 165 (5825 MHz), width: 20 MHz, center1: 5825 MHz
	txpower 24.00 dBm
	multicast TXQ:
		qsz-byt	qsz-pkt	flows	drops	marks	overlmt	hashcol	tx-bytes	tx-packets
		0	0	72	0	0	0	0	7380		72

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>