idpf: skip deallocating txq group's txqs if it is NULL

idpf: skip deallocating txq group's txqs if it is NULL

In idpf_txq_group_alloc(), if any txq group's txqs failed to
allocate memory:

	for (j = 0; j < tx_qgrp->num_txq; j++) {
		tx_qgrp->txqs[j] = kzalloc(sizeof(*tx_qgrp->txqs[j]),
					   GFP_KERNEL);
		if (!tx_qgrp->txqs[j])
			goto err_alloc;
	}

It would cause a NULL ptr kernel panic in idpf_txq_group_rel():

	for (j = 0; j < txq_grp->num_txq; j++) {
		if (flow_sch_en) {
			kfree(txq_grp->txqs[j]->refillq);
			txq_grp->txqs[j]->refillq = NULL;
		}

		kfree(txq_grp->txqs[j]);
		txq_grp->txqs[j] = NULL;
	}

[    6.532461] BUG: kernel NULL pointer dereference, address: 0000000000000058
...
[    6.534433] RIP: 0010:idpf_txq_group_rel+0xc9/0x110
...
[    6.538513] Call Trace:
[    6.538639]  <TASK>
[    6.538760]  idpf_vport_queues_alloc+0x75/0x550
[    6.538978]  idpf_vport_open+0x4d/0x3f0
[    6.539164]  idpf_open+0x71/0xb0
[    6.539324]  __dev_open+0x142/0x260
[    6.539506]  netif_open+0x2f/0xe0
[    6.539670]  dev_open+0x3d/0x70
[    6.539827]  bond_enslave+0x5ed/0xf50
[    6.540005]  ? rcutree_enqueue+0x1f/0xb0
[    6.540193]  ? call_rcu+0xde/0x2a0
[    6.540375]  ? barn_get_empty_sheaf+0x5c/0x80
[    6.540594]  ? __kfree_rcu_sheaf+0xb6/0x1a0
[    6.540793]  ? nla_put_ifalias+0x3d/0x90
[    6.540981]  ? kvfree_call_rcu+0xb5/0x3b0
[    6.541173]  ? kvfree_call_rcu+0xb5/0x3b0
[    6.541365]  do_set_master+0x114/0x160
[    6.541547]  do_setlink+0x412/0xfb0
[    6.541717]  ? security_sock_rcv_skb+0x2a/0x50
[    6.541931]  ? sk_filter_trim_cap+0x7c/0x320
[    6.542136]  ? skb_queue_tail+0x20/0x50
[    6.542322]  ? __nla_validate_parse+0x92/0xe50
ro[o t   t o6 .d5e4f2a5u4l0t]-  ? security_capable+0x35/0x60
[    6.542792]  rtnl_newlink+0x95c/0xa00
[    6.542972]  ? __rtnl_unlock+0x37/0x70
[    6.543152]  ? netdev_run_todo+0x63/0x530
[    6.543343]  ? allocate_slab+0x280/0x870
[    6.543531]  ? security_capable+0x35/0x60
[    6.543722]  rtnetlink_rcv_msg+0x2e6/0x340
[    6.543918]  ? __pfx_rtnetlink_rcv_msg+0x10/0x10
[    6.544138]  netlink_rcv_skb+0x16a/0x1a0
[    6.544328]  netlink_unicast+0x20a/0x320
[    6.544516]  netlink_sendmsg+0x304/0x3b0
[    6.544748]  __sock_sendmsg+0x89/0xb0
[    6.544928]  ____sys_sendmsg+0x167/0x1c0
[    6.545116]  ? ____sys_recvmsg+0xed/0x150
[    6.545308]  ___sys_sendmsg+0xdd/0x120
[    6.545489]  ? ___sys_recvmsg+0x124/0x1e0
[    6.545680]  ? rcutree_enqueue+0x1f/0xb0
[    6.545867]  ? rcutree_enqueue+0x1f/0xb0
[    6.546055]  ? call_rcu+0xde/0x2a0
[    6.546222]  ? evict+0x286/0x2d0
[    6.546389]  ? rcutree_enqueue+0x1f/0xb0
[    6.546577]  ? kmem_cache_free+0x2c/0x350
[    6.546784]  __x64_sys_sendmsg+0x72/0xc0
[    6.546972]  do_syscall_64+0x6f/0x890
[    6.547150]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[    6.547393] RIP: 0033:0x7fc1a3347bd0
...
[    6.551375] RIP: 0010:idpf_txq_group_rel+0xc9/0x110
...
[    6.578856] Rebooting in 10 seconds..

We should skip deallocating txqs[j] if it is NULL in the first place.

Tested: with this patch, the kernel panic no longer appears.

Fixes: 1c325aac10a8 ("idpf: configure resources for TX queues")
Signed-off-by: Li Li <boolli@google.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Samuel Salin <Samuel.salin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>