Add VIR_DOMAIN_DEVICE_MODIFY_LIVE to extconf consts.
Add VIR_DOMAIN_DEVICE_MODIFY_LIVE to extconf consts.

Otherwise, HAVE_CONST_VIR_DOMAIN_DEVICE_MODIFY_LIVE is
never true and we don't define the constant.  Pointed
out by Neil Wilson.

Signed-off-by: Chris Lalancette <60b62644009db6b194cc0445b64e9b27bb26433a@redhat.com>

pronix/ruby-libvirt,pronix/ruby-libvirt,pronix/ruby-libvirt