bonding: hold ops lock around get_link

bonding: hold ops lock around get_link

syzbot reports a case of ethtool_ops->get_link being called without
ops lock:

 ethtool_op_get_link+0x15/0x60 net/ethtool/ioctl.c:63
 bond_check_dev_link+0x1fb/0x4b0 drivers/net/bonding/bond_main.c:864
 bond_miimon_inspect drivers/net/bonding/bond_main.c:2734 [inline]
 bond_mii_monitor+0x49d/0x3170 drivers/net/bonding/bond_main.c:2956
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xac3/0x18e0 kernel/workqueue.c:3319
 worker_thread+0x870/0xd50 kernel/workqueue.c:3400
 kthread+0x7b7/0x940 kernel/kthread.c:464
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Commit 04efcee6ef8d ("net: hold instance lock during NETDEV_CHANGE")
changed to lockless __linkwatch_sync_dev in ethtool_op_get_link.
All paths except bonding are coming via locked ioctl. Add necessary
locking to bonding.

Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Reported-by: syzbot+48c14f61594bdfadb086@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=48c14f61594bdfadb086
Fixes: 04efcee6ef8d ("net: hold instance lock during NETDEV_CHANGE")
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250410161117.3519250-1-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>