Networking-related fixes
- bx_param_string_c method isempty() didn't work for raw byte strings. Now using
  it to check whether or not the current value matches the initial one. The
  parameter handling of the network adapters now use this method to check if
  the MAC address is already initialized to avoid incorrect BX_ERRORs.
- small documentation update


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12236 6c8e4198-a580-4521-a02f-c9ae86df1db9