Overall:

• Updated license headers to be in sync with recent changes in FreeBSD base (see r314436)
• Now builds shared library, as libifconfig is marked as private

libifconfig.c:

• Added support for creating general virtual interfaces, and vlan interfaces.
• Added support for configuring vlandev/vlanid on an unconfigured vlan interface.
• Fixed potential NULL reference in ifconfig_open()
• ifconfig_get_description():
  • Fixed memory leak
  • Fixed errornous return value when strdup() fails to set 'description'
• Some if statements were incorrectly linewrapped even though they were short enough to be on one line.

libifconfig_internal.c:

• Morphed function ifconfig_ioctlwrap_ret(...) into ifconfig_ioctlwrap(...), as that's the only function needing that functionality now

Submitted by: Marie Helene Kvello-Aune <marieheleneka@gmail.com>