get_interfaces() updated to read /proc/net/dev.  This means it no
longer provides only interfaces that are up.

get_iface_hwaddr() updated to read from /sys/class/net/<iface>/address.

Added get_interface_facts() to pull in mac address and interface mtu.
Can be used later for additional interface-facts.

Added get_ipv6_facts(), which reads from /proc/net/if_inet6.

get_network_facts() renamed to get_ipv4_facts().  It still calls
ifconfig to determine ipv4 facts.