bridge: br_vlan_fill_forward_path_pvid: use br_vlan_group_rcu()

bridge: br_vlan_fill_forward_path_pvid: use br_vlan_group_rcu()

net/bridge/br_private.h:1627 suspicious rcu_dereference_protected() usage!
other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
7 locks held by socat/410:
 #0: ffff88800d7a9c90 (sk_lock-AF_INET){+.+.}-{0:0}, at: inet_stream_connect+0x43/0xa0
 #1: ffffffff9a779900 (rcu_read_lock){....}-{1:3}, at: __ip_queue_xmit+0x62/0x1830
 [..]
 #6: ffffffff9a779900 (rcu_read_lock){....}-{1:3}, at: nf_hook.constprop.0+0x8a/0x440

Call Trace:
 lockdep_rcu_suspicious.cold+0x4f/0xb1
 br_vlan_fill_forward_path_pvid+0x32c/0x410 [bridge]
 br_fill_forward_path+0x7a/0x4d0 [bridge]

Use to correct helper, non _rcu variant requires RTNL mutex.

Fixes: bcf2766b1377 ("net: bridge: resolve forwarding path for VLAN tag actions in bridge devices")
Signed-off-by: Eric Woudstra <ericwouds@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>