tool/wr-streamers implement missing commands + couple of fixes

- new command "ls" (leapsecond to overwrite the default value
- implement get_set_tx_local_mac, get_set_tx_remote_mac
  get_set_rx_ethertype get_set_rx_local_mac, get_set_rx_remote_mac,

Signed-off-by: Michel Arruat <michel.arruat@cern.ch>