Lockdep found an inconsistent lock state when mtk_get_stats64 is called
in user context while NAPI updates MAC statistics in softirq.

Use spin_trylock_bh/spin_unlock_bh fix following lockdep warning.

[   81.321030] WARNING: inconsistent lock state
[   81.325266] 4.12.0-rc1-00035-gd9dda65 #32 Not tainted
[   81.330273] --------------------------------
[   81.334505] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
[   81.340464] ksoftirqd/0/7 [HC0[0]:SC1[1]:HE1:SE0] takes:
[   81.345731]  (&syncp->seq#2){+.?...}, at: [<c054ba3c>] mtk_handle_status_irq.part.6+0x70/0x84
[   81.354219] {SOFTIRQ-ON-W} state was registered at:
[   81.359062]   lock_acquire+0xfc/0x2b0
[   81.362696]   mtk_stats_update_mac+0x60/0x2c0
[   81.367017]   mtk_get_stats64+0x17c/0x18c
[   81.370995]   dev_get_stats+0x48/0xbc
[   81.374628]   rtnl_fill_stats+0x48/0x128
[   81.378520]   rtnl_fill_ifinfo+0x4ac/0xd1c
[   81.382584]   rtmsg_ifinfo_build_skb+0x7c/0xe0
[   81.386991]   rtmsg_ifinfo.part.5+0x24/0x54
[   81.391139]   rtmsg_ifinfo+0x24/0x28
[   81.394685]   __dev_notify_flags+0xa4/0xac
[   81.398749]   dev_change_flags+0x50/0x58
[   81.402640]   devinet_ioctl+0x768/0x85c
[   81.406444]   inet_ioctl+0x1a4/0x1d0
[   81.409990]   sock_ioctl+0x16c/0x33c
[   81.413538]   do_vfs_ioctl+0xb4/0xa34
[   81.417169]   SyS_ioctl+0x44/0x6c
[   81.420458]   ret_fast_syscall+0x0/0x1c
[   81.424260] irq event stamp: 3354692
[   81.427806] hardirqs last  enabled at (3354692): [<c0678168>] net_rx_action+0xc0/0x504
[   81.435660] hardirqs last disabled at (3354691): [<c0678134>] net_rx_action+0x8c/0x504
[   81.443515] softirqs last  enabled at (3354106): [<c0101944>] __do_softirq+0x4b4/0x614
[   81.451370] softirqs last disabled at (3354109): [<c012f0c4>] run_ksoftirqd+0x44/0x80
[   81.459134]
[   81.459134] other info that might help us debug this:
[   81.465608]  Possible unsafe locking scenario:
[   81.465608]
[   81.471478]        CPU0
[   81.473900]        ----
[   81.476321]   lock(&syncp->seq#2);
[   81.479701]   <Interrupt>
[   81.482294]     lock(&syncp->seq#2);
[   81.485847]
[   81.485847]  *** DEADLOCK ***
[   81.485847]
[   81.491720] 1 lock held by ksoftirqd/0/7:
[   81.495693]  #0:  (&(&mac->hw_stats->stats_lock)->rlock){+.+...}, at: [<c054ba14>] mtk_handle_status_irq.part.6+0x48/0x84
[   81.506579]
[   81.506579] stack backtrace:
[   81.510904] CPU: 0 PID: 7 Comm: ksoftirqd/0 Not tainted 4.12.0-rc1-00035-gd9dda65 #32
[   81.518668] Hardware name: Mediatek Cortex-A7 (Device Tree)
[   81.524208] [<c0113dc4>] (unwind_backtrace) from [<c010e3f0>] (show_stack+0x20/0x24)
[   81.531899] [<c010e3f0>] (show_stack) from [<c03f9c64>] (dump_stack+0xb4/0xe0)
[   81.539072] [<c03f9c64>] (dump_stack) from [<c017e970>] (print_usage_bug+0x234/0x2e0)
[   81.546846] [<c017e970>] (print_usage_bug) from [<c017f058>] (mark_lock+0x63c/0x7bc)
[   81.554532] [<c017f058>] (mark_lock) from [<c017fe90>] (__lock_acquire+0x654/0x1bfc)
[   81.562217] [<c017fe90>] (__lock_acquire) from [<c0181d04>] (lock_acquire+0xfc/0x2b0)
[   81.569990] [<c0181d04>] (lock_acquire) from [<c054b76c>] (mtk_stats_update_mac+0x60/0x2c0)
[   81.578283] [<c054b76c>] (mtk_stats_update_mac) from [<c054ba3c>] (mtk_handle_status_irq.part.6+0x70/0x84)
[   81.587865] [<c054ba3c>] (mtk_handle_status_irq.part.6) from [<c054c2b8>] (mtk_napi_tx+0x358/0x37c)
[   81.596845] [<c054c2b8>] (mtk_napi_tx) from [<c06782ec>] (net_rx_action+0x244/0x504)
[   81.604533] [<c06782ec>] (net_rx_action) from [<c01015c4>] (__do_softirq+0x134/0x614)
[   81.612306] [<c01015c4>] (__do_softirq) from [<c012f0c4>] (run_ksoftirqd+0x44/0x80)
[   81.619907] [<c012f0c4>] (run_ksoftirqd) from [<c0154680>] (smpboot_thread_fn+0x14c/0x25c)
[   81.628110] [<c0154680>] (smpboot_thread_fn) from [<c014f8cc>] (kthread+0x150/0x180)
[   81.635798] [<c014f8cc>] (kthread) from [<c0109290>] (ret_from_fork+0x14/0x24)
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>