[master] Merge branch 'trac3982' (Decline v6)
Conflicts: src/bin/dhcp6/dhcp6_srv.cc src/lib/dhcpsrv/lease.cc src/lib/dhcpsrv/tests/lease_unittest.cc
Conflicts: src/bin/dhcp6/dhcp6_srv.cc src/lib/dhcpsrv/lease.cc src/lib/dhcpsrv/tests/lease_unittest.cc