refactor: improve network interface validation

Add context parameter to validInterfacesMap for better error handling and
logging. Move Windows-specific network adapter validation logic to the
ctrld package. Key changes include:

- Add context parameter to validInterfacesMap across all platforms
- Move Windows validInterfaces to ctrld.ValidInterfaces
- Improve error handling for virtual interface detection on Linux
- Update all callers to pass appropriate context

This change improves error reporting and makes the interface validation
code more maintainable across different platforms.

cmd/cli/net_others.go

@@ -3,6 +3,7 @@
 package cli
 
 import (
+	"context"
 	"net"
 
 	"tailscale.com/net/netmon"
@@ -13,7 +14,7 @@ func patchNetIfaceName(iface *net.Interface) (bool, error) { return true, nil }
 func validInterface(iface *net.Interface, validIfacesMap map[string]struct{}) bool { return true }
 
 // validInterfacesMap returns a set containing only default route interfaces.
-func validInterfacesMap() map[string]struct{} {
+func validInterfacesMap(ctx context.Context) map[string]struct{} {
 	defaultRoute, err := netmon.DefaultRoute()
 	if err != nil {
 		return nil