compat: support dummy interface

Parsing of ifcfg files belonging to dummy interfaces.
ifconfig: provide dummy system functions

System functions for creating, changing and deleting dummy interfaces.
ifconfig: return netlink error code if link create fails

Since the errors are returned in their negative forms, current checks
for 0, less than 0, etc, work fine.

This is currently useful for Dummy interface creation since loading the
dummy kernel module automatically creates a dummy0 interface. If the user
tries to create another via ifcfg/xml, checking for -NLE_EXISTS allows us
to better handle this case from ni_system_dummy_create().
dbus: dummy interface dbus service

Support for creating dummy network interfaces.
dbus: enable dummy dbus service
Merge pull request #192 from kmroz/dummy-rc2
dummy: added dummy and static-mac bridge examples
bridge: lowered a questionable warning to debug
netlink: fixed masterdev reference name resolving

It were using the lowerdev variable instead of masterdev,
causing warning about unknown master device reference.
Also lowered warning to info as we ignore and proceed...
utils: added a start number to netdev make name

We'll need it later, e.g. for tunnels.
tun: initial support, no ifcfg yet
tap: initial support, no ifcfg yet

Merge with existing TUN and change to TUN/TAP (tuntap) when possible
to avoid code duplications.
compat: Add ifcfg tunnel support
Merge pull request #193 from pwieczorkiewicz/tuntap

Add TUN/TAP support
version 0.5.15
addrconf: drop default route if disabled (bnc#868187)

Honor a (per-interface) DHCLIENT_SET_DEFAULT_ROUTE=no in
suse ifcfg files and remove from lease before update runs.