net/net_failover: fix txq exceeding warning

net/net_failover: fix txq exceeding warning

The failover txq is inited as 16 queues.
when a packet is transmitted from the failover device firstly,
the failover device will select the queue which is returned from
the primary device if the primary device is UP and running.
If the primary device txq is bigger than the default 16,
it can lead to the following warning:
eth0 selects TX queue 18, but real number of TX queues is 16

The warning backtrace is:
[   32.146376] CPU: 18 PID: 9134 Comm: chronyd Tainted: G            E      6.2.8-1.el7.centos.x86_64 #1
[   32.147175] Hardware name: Red Hat KVM, BIOS 1.10.2-3.el7_4.1 04/01/2014
[   32.147730] Call Trace:
[   32.147971]  <TASK>
[   32.148183]  dump_stack_lvl+0x48/0x70
[   32.148514]  dump_stack+0x10/0x20
[   32.148820]  netdev_core_pick_tx+0xb1/0xe0
[   32.149180]  __dev_queue_xmit+0x529/0xcf0
[   32.149533]  ? __check_object_size.part.0+0x21c/0x2c0
[   32.149967]  ip_finish_output2+0x278/0x560
[   32.150327]  __ip_finish_output+0x1fe/0x2f0
[   32.150690]  ip_finish_output+0x2a/0xd0
[   32.151032]  ip_output+0x7a/0x110
[   32.151337]  ? __pfx_ip_finish_output+0x10/0x10
[   32.151733]  ip_local_out+0x5e/0x70
[   32.152054]  ip_send_skb+0x19/0x50
[   32.152366]  udp_send_skb.isra.0+0x163/0x3a0
[   32.152736]  udp_sendmsg+0xba8/0xec0
[   32.153060]  ? __folio_memcg_unlock+0x25/0x60
[   32.153445]  ? __pfx_ip_generic_getfrag+0x10/0x10
[   32.153854]  ? sock_has_perm+0x85/0xa0
[   32.154190]  inet_sendmsg+0x6d/0x80
[   32.154508]  ? inet_sendmsg+0x6d/0x80
[   32.154838]  sock_sendmsg+0x62/0x70
[   32.155152]  ____sys_sendmsg+0x134/0x290
[   32.155499]  ___sys_sendmsg+0x81/0xc0
[   32.155828]  ? _get_random_bytes.part.0+0x79/0x1a0
[   32.156240]  ? ip4_datagram_release_cb+0x5f/0x1e0
[   32.156649]  ? get_random_u16+0x69/0xf0
[   32.156989]  ? __fget_light+0xcf/0x110
[   32.157326]  __sys_sendmmsg+0xc4/0x210
[   32.157657]  ? __sys_connect+0xb7/0xe0
[   32.157995]  ? __audit_syscall_entry+0xce/0x140
[   32.158388]  ? syscall_trace_enter.isra.0+0x12c/0x1a0
[   32.158820]  __x64_sys_sendmmsg+0x24/0x30
[   32.159171]  do_syscall_64+0x38/0x90
[   32.159493]  entry_SYSCALL_64_after_hwframe+0x72/0xdc

Fix that by reducing txq number as the non-existent primary-dev does.

Fixes: cfc80d9a1163 ("net: Introduce net_failover driver")
Signed-off-by: Faicker Mo <faicker.mo@ucloud.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>