fix defaults for non-specified streams

tangostationcontrol/tangostationcontrol/devices/sdp/beamlet.py

@@ -657,8 +657,8 @@ class Beamlet(OPCUADevice):
 
         # Set MAC, IP, port
         for setting, value_if_undefined in [
-            ("FPGA_beamlet_output_multiple_hdr_eth_destination_mac_RW", ""),
-            ("FPGA_beamlet_output_multiple_hdr_ip_destination_address_RW", ""),
+            ("FPGA_beamlet_output_multiple_hdr_eth_destination_mac_RW", "00:00:00:00:00:00"),
+            ("FPGA_beamlet_output_multiple_hdr_ip_destination_address_RW", "0.0.0.0"),
             ("FPGA_beamlet_output_multiple_hdr_udp_destination_port_RW", 0),
         ]:
             # obtain shorthand description (first values per fpga)