domifaddr: Implement the public APIs

domifaddr: Implement the public APIs

Define helper function virDomainInterfaceFree, which allows
the upper layer application to free the domain interface object
conveniently.

The API is going to provide multiple methods by flags, e.g.
  * Query guest agent
  * Parse DHCP lease file

include/libvirt/libvirt-domain.h
  * Define virDomainInterfaceAddresses, virDomainInterfaceFree
  * Define structs virDomainInterface, virDomainIPAddress

src/driver-hypervisor.h:
  * Define domainInterfaceAddresses

src/libvirt-domain.c:
  * Implement virDomainInterfaceAddresses
  * Implement virDomainInterfaceFree

src/libvirt_public.syms:
  * Export the new symbols

Signed-off-by: Nehal J Wani <nehaljw.kkd1@gmail.com>