When configuring TC-MQPRIO offload, only turn off netdev carrier and
don't bring physical link down in hardware. Otherwise, when the
physical link is brought up again after configuration, it gets
re-trained and stalls ongoing traffic.

Also, when firmware is no longer accessible or crashed, avoid sending
FLOWC and waiting for reply that will never come.

Fix following hung_task_timeout_secs trace seen in these cases.

INFO: task tc:20807 blocked for more than 122 seconds.
      Tainted: G S                5.13.0-rc3+ #122
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:tc   state:D stack:14768 pid:20807 ppid: 19366 flags:0x00000000
Call Trace:
 __schedule+0x27b/0x6a0
 schedule+0x37/0xa0
 schedule_preempt_disabled+0x5/0x10
 __mutex_lock.isra.14+0x2a0/0x4a0
 ? netlink_lookup+0x120/0x1a0
 ? rtnl_fill_ifinfo+0x10f0/0x10f0
 __netlink_dump_start+0x70/0x250
 rtnetlink_rcv_msg+0x28b/0x380
 ? rtnl_fill_ifinfo+0x10f0/0x10f0
 ? rtnl_calcit.isra.42+0x120/0x120
 netlink_rcv_skb+0x4b/0xf0
 netlink_unicast+0x1a0/0x280
 netlink_sendmsg+0x216/0x440
 sock_sendmsg+0x56/0x60
 __sys_sendto+0xe9/0x150
 ? handle_mm_fault+0x6d/0x1b0
 ? do_user_addr_fault+0x1c5/0x620
 __x64_sys_sendto+0x1f/0x30
 do_syscall_64+0x3c/0x80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f7f73218321
RSP: 002b:00007ffd19626208 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 000055b7c0a8b240 RCX: 00007f7f73218321
RDX: 0000000000000028 RSI: 00007ffd19626210 RDI: 0000000000000003
RBP: 000055b7c08680ff R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000055b7c085f5f6
R13: 000055b7c085f60a R14: 00007ffd19636470 R15: 00007ffd196262a0

Fixes: b1396c2bd675 ("cxgb4: parse and configure TC-MQPRIO offload")
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>