move platformGetRTT implementation to tcp_common.go for non-Linux platforms

pkg/interfaces/tcp_common.go

@@ -2,3 +2,13 @@
 // +build !linux
 
 package interfaces
+
+import (
+	"time"
+)
+
+// platformGetRTT is defined in OS-specific files
+// Default implementation for non-Linux platforms
+func platformGetRTT(fd uintptr) time.Duration {
+	return 0
+}