btsnoop_net: Fix instruction for btsnoop logs

btsnoop_net exposes Bluetooth snoop logs over a local TCP socket which enables

real-time debugging of HCI data with hcidump.

This feature is enabled by  setting `BtSnoopLogOutput=true` in `bt_stack.conf`.

This feature is enabled by  enabling  "Enable Bluetooth HCI snoop log" in the

Developer options and setting BT_NET_DEBUG flag to TRUE in the btsnoop_net.cc.

Once it has been enabled and the stack restarted, the stack will listen for

incoming TCP connections on port 8872.

To use this feature with hcidump on a Linux host, you can run:

To use this feature with btmon on a Linux host, you can run:

```

  $ adb forward tcp:8872 tcp:8872

  $ nc localhost 8872 | hcidump -r /dev/stdin

  $ nc localhost 8872 | btmon -P -r /dev/stdin

```