ipdb: use watchdog instead of wait_interface

Separate watchdog setup and wait makes more clear semantics.
ipdb: increase _SYNC_TIMEOUT from 3 to 5s
ipdb: throw CommitException instead of AssertionError
ipdb: filter out IPv6 link-local from ipaddr.target
tests: fix IPDB interface-level callbacks
ipdb: sync targets for specific fields
tests: bonding mode 2