Implement global configuration

[brgerig]

I tested and verified that global configurations are working in lldpad v0.9.46. It created a "common:" section in the lldpad.conf file, and applied any configuration directives there to all interfaces:

lldp:
{
  eth0 :
  <snipped>
  common :
  {
    adminStatus = 3;
    tlvid00000005 :
    {
      enableTx = true;
    };
    tlvid00000004 :
    {
      enableTx = true;
    };
    tlvid00000006 :
    {
      enableTx = true;
    };
    tlvid00000008 :
    {
      enableTx = true;
    };
    tlvid00000007 :
    {
      enableTx = true;
    };
  };
};

[razorsedge]

Looks like something for the TODO list.