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This is trivial fix so as I am committing it on my own discretion. Also,
this fix had already been reviewed and applied on master branch but
apparently disappeared after the recent git migration.

Also, fixed selection of the unicast addresses for receiving DHCP packets.

Also, added better documentation for the IfaceCfg class.

This change affects DHCP servers and D2.

Changes include documenting the constants used for selection of parameters
to be reported by getConfigSummary and a todo.

 - Daemon::getVersion() added
 - exists => exits in docs
 - fixed comment in dhcp_test_lib.sh.in

 - variables, test renamed in daemon unit-tests
 - verbose parameter documented in Daemon class