Separated (and renamed) WriteUdevDriverRules

Separated into two functions. First writes per interface udev rules
(device renaming). Second writes per driver udev rules.
Added helper for getting iface's udev rule.
Fixed and refactored WriteUdevItemsRules.

Contains several improvements. Most important are
- when writing udev rule for particular interface, network service
needn't be stopped, setting iface down is enough
- udev rules are reloaded after writing them down, so the daemon
can reflect changes
- when trigger(ing) udev events, explicit action identification was
added (default has changed in the past from add -> change)