netstat, portlist: update Windows implementation to disambiguate svchost processes

We change our invocations of GetExtendedTcpTable to request additional
information about the "module" responsible for the port. In addition to pid,
this output also includes sufficient metadata to enable Windows to resolve
process names and disambiguate svchost processes.

We store the OS-specific output in an OSMetadata field in netstat.Entry, which
portlist may then use as necessary to actually resolve the process/module name.

Signed-off-by: Aaron Klotz <aaron@tailscale.com>

net/netstat/netstat.go

@@ -17,6 +17,7 @@ type Entry struct {
 	Local, Remote netip.AddrPort
 	Pid           int
 	State         string // TODO: type?
+	OSMetadata    OSMetadata
 }
 
 // Table contains local machine's TCP connection entries.