[master] Merge branch 'trac3695'

diff --cc doc/guide/dhcp4-srv.xml
Simple merge

diff --cc src/bin/dhcp4/dhcp4_srv.cc
Simple merge

diff --cc src/bin/dhcp4/tests/dhcp4_srv_unittest.cc
Simple merge

diff --cc src/lib/dhcp/iface_mgr.cc
Simple merge

diff --cc src/lib/dhcp/iface_mgr.h
Simple merge

diff --cc src/lib/dhcp/tests/iface_mgr_unittest.cc
Simple merge

diff --cc src/lib/dhcpsrv/dhcpsrv_messages.mes
Simple merge