src/lib/dhcp/tests/pkt_filter_test_stub.cc
 - PktFilterTestStub::openSocket() - the filter's SocketInfo::sock_fd_ is
   now set with value returend by opening "/dev/null" as read_only.  This
   provides a valid, consumed fd that the filter retains until its socket
   is closed.

src/bin/dhcp4/tests/ctrl_dhcp4_srv_unittest.cc
    CtrlChannelDhcp4SrvTest removed the fd/0 work-around as it is no
    longer needed
~