ip: iplink_bridge: Support bridge VLAN stats in `ip stats'

ip: iplink_bridge: Support bridge VLAN stats in `ip stats'

Add support for displaying bridge VLAN statistics in `ip stats'.
Reuse the existing `bridge vlan' display and JSON format:

 # ip stats show dev v2 group xstats_slave subgroup bridge suite vlan
 2: v2: group xstats_slave subgroup bridge suite vlan
                   10
                     RX: 3376 bytes 50 packets
                     TX: 2824 bytes 44 packets

                   20
                     RX: 684 bytes 7 packets
                     TX: 0 bytes 0 packets

 # ip -j -p stats show dev v2 group xstats_slave subgroup bridge suite vlan
 [ {
         "ifindex": 2,
         "ifname": "v2",
         "group": "xstats_slave",
         "subgroup": "bridge",
         "suite": "vlan",
         "vlans": [ {
                 "vid": 10,
                 "rx_bytes": 3376,
                 "rx_packets": 50,
                 "tx_bytes": 2824,
                 "tx_packets": 44
             },{
                 "vid": 20,
                 "rx_bytes": 684,
                 "rx_packets": 7,
                 "tx_bytes": 0,
                 "tx_packets": 0
             } ]
     } ]

Similarly for the master stats:

 # ip stats show dev br1 group xstats subgroup bridge suite vlan
 211: br1: group xstats subgroup bridge suite vlan
                   10
                     RX: 3376 bytes 50 packets
                     TX: 2824 bytes 44 packets

                   20
                     RX: 684 bytes 7 packets
                     TX: 0 bytes 0 packets

 # ip -j -p stats show dev br1 group xstats subgroup bridge suite vlan
 [ {
         "ifindex": 211,
         "ifname": "br1",
         "group": "xstats",
         "subgroup": "bridge",
         "suite": "vlan",
         "vlans": [ {
                 "vid": 10,
                 "flags": [ ],
                 "rx_bytes": 3376,
                 "rx_packets": 50,
                 "tx_bytes": 2824,
                 "tx_packets": 44
             },{
                 "vid": 20,
                 "flags": [ ],
                 "rx_bytes": 684,
                 "rx_packets": 7,
                 "tx_bytes": 0,
                 "tx_packets": 0
             } ]
     } ]

Signed-off-by: Petr Machata <petrm@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David Ahern <dsahern@kernel.org>