Disable opening network debug ports for security reasons

By default, we open up to three TCP ports that are used
for debugging purpose:

 * TCP port 8872 - used for forwarding btsnoop logs at real time
   Note: the port is open only if "Bluetooth HCI snoop log" is enabled
   in the Developer options
 * TCP port 8873 - used for HCI debugging
 * TCP port 8879 - used for debugging the Bluetooth counters

Those ports are disabled by default.
To enable, the following #define should be added at the top of the
corresponding file(s): btcore/src/counter.c hci/src/btsnoop_net.c
hci/src/hci_inject.c

   #define BT_NET_DEBUG TRUE

Bug: 24371736

Change-Id: I5cb43af1a5d29c331eb5ef61a24dccbe95df6f40