tcpip: ignore network with a netmask set to None (#478)

* tcpip: ignore network with a netmask set to None

For such netmask, the mask is 32 bits long per psutil docs and

* update release notes

CHANGES

@@ -4,6 +4,9 @@ PyVISA-py Changelog
 0.7.3 (unreleased)
 ------------------
 
+- ignore network interface card with no subnet mask when discovering TCPIP
+  resources PR #478
+- add VICP INSTR to the supported interface for TCPIP keep alive attr PR #477
 - add read_stb method for TCPIP HiSLIP client PR #429
 - fix usbtmc implementation to respect section 3.3 of the spec PR #449
   Read now reads from usb until a "short packet" or if all data (`transfer_size`) PR #465

pyvisa_py/tcpip.py

@@ -419,7 +419,7 @@ def list_resources() -> List[str]:
             # Get broadcast address for each interface
             for interface, snics in psutil.net_if_addrs().items():
                 for snic in snics:
-                    if snic.family is socket.AF_INET:
+                    if snic.family is socket.AF_INET and snic.netmask is not None:
                         addr = snic.address
                         mask = snic.netmask
                         network = ipaddress.IPv4Network(addr + "/" + mask, strict=False)