Replace Network Type string with Const in ResourceMonitoring (#5398)

* Replace Network Type string with Const in ResourceMonitoring

* Apply the change to LinuxNetworkMetrics.cs as well

---------

Co-authored-by: Yifan Zhu <yifzhu@microsoft.com>

src/Libraries/Microsoft.Extensions.Diagnostics.ResourceMonitoring/Linux/Network/LinuxNetworkMetrics.cs

@@ -37,11 +37,12 @@ public LinuxNetworkMetrics(IMeterFactory meterFactory, ITcpStateInfoProvider tcp
 
     private IEnumerable<Measurement<long>> GetMeasurements()
     {
+        const string NetworkTypeKey = "network.type";
         const string NetworkStateKey = "system.network.state";
 
         // These are covered in https://github.com/open-telemetry/semantic-conventions/blob/main/docs/rpc/rpc-metrics.md#attributes:
-        KeyValuePair<string, object?> tcpVersionFourTag = new("network.type", "ipv4");
-        KeyValuePair<string, object?> tcpVersionSixTag = new("network.type", "ipv6");
+        KeyValuePair<string, object?> tcpVersionFourTag = new(NetworkTypeKey, "ipv4");
+        KeyValuePair<string, object?> tcpVersionSixTag = new(NetworkTypeKey, "ipv6");
 
         List<Measurement<long>> measurements = new(24);
 

src/Libraries/Microsoft.Extensions.Diagnostics.ResourceMonitoring/Windows/Network/WindowsNetworkMetrics.cs

@@ -37,11 +37,12 @@ public WindowsNetworkMetrics(IMeterFactory meterFactory, ITcpStateInfoProvider t
 
     private IEnumerable<Measurement<long>> GetMeasurements()
     {
+        const string NetworkTypeKey = "network.type";
         const string NetworkStateKey = "system.network.state";
 
         // These are covered in https://github.com/open-telemetry/semantic-conventions/blob/main/docs/rpc/rpc-metrics.md#attributes:
-        KeyValuePair<string, object?> tcpVersionFourTag = new("network.type", "ipv4");
-        KeyValuePair<string, object?> tcpVersionSixTag = new("network.type", "ipv6");
+        KeyValuePair<string, object?> tcpVersionFourTag = new(NetworkTypeKey, "ipv4");
+        KeyValuePair<string, object?> tcpVersionSixTag = new(NetworkTypeKey, "ipv6");
 
         List<Measurement<long>> measurements = new(24);