add option to show kfree_skb call stack

[curu]

For kernel versions that do not support drop reason, or drop point that has not yet been traced, it may be helpful to show the call stack of kfree_skb, so that we can infer the drop reason.

eg:

nettrace -p udp --diag  --diag-quiet --diag-stack
...
[1] ERROR happens in kfree_skb(life):
    packet is dropped by kernel
    location:
    __udp4_lib_rcv+0x8fe
    stack:
       __udp4_lib_rcv ([kernel.kallsyms])
       ip_protocol_deliver_rcu ([kernel.kallsyms])
       ip_local_deliver_finish ([kernel.kallsyms])
       ip_local_deliver ([kernel.kallsyms])
       ip_rcv_finish ([kernel.kallsyms])
       ip_rcv ([kernel.kallsyms])
       __netif_receive_skb_core ([kernel.kallsyms])
       __netif_receive_skb_list_core ([kernel.kallsyms])
       netif_receive_skb_list_internal ([kernel.kallsyms])
       gro_normal_list.part.143 ([kernel.kallsyms])
       napi_complete_done ([kernel.kallsyms])
       virtnet_poll ([kernel.kallsyms])
       net_rx_action ([kernel.kallsyms])

[menglongdong]

已完成支持：

nettrace -p tcp --drop --drop-stack 
begin trace...
[2114.791575] TCP: 127.0.0.1:46544 -> 127.0.0.1:9999 seq:714874229, ack:0, flags:S, tcp_v4_rcv+0x63
Call Stack:
    -> kfree_skb_reason+0xb8
    -> kfree_skb_reason+0xb8
    -> tcp_v4_rcv+0x63
    -> ip_protocol_deliver_rcu+0x30
    -> ip_local_deliver_finish+0x48
    -> ip_local_deliver+0xcb
    -> ip_rcv_finish+0x83
    -> ip_rcv+0xb1
    -> __netif_receive_skb_one_core+0x85
    -> process_backlog+0x9e
    -> napi_poll+0x9d
    -> net_rx_action+0xac
    -> __softirqentry_text_start+0xdd
    -> do_softirq_own_stack+0x2a
    -> do_softirq+0x41
    -> __local_bh_enable_ip+0x50
    -> ip_finish_output2+0x1be
    -> __ip_finish_output+0xb0
    -> ip_finish_output+0x36
    -> ip_output+0x6b
    -> __ip_queue_xmit+0x18c
    -> ip_queue_xmit+0x10
    -> __tcp_transmit_skb+0x528
    -> tcp_connect+0x34e
    -> tcp_v4_connect+0x3d8
    -> __inet_stream_connect+0xd3
    -> inet_stream_connect+0x3b
    -> __sys_connect+0xab
    -> __x64_sys_connect+0x18
    -> do_syscall_64+0x49
    -> entry_SYSCALL_64_after_hwframe+0x44