Update a comment.

I backed pcap_handle() out; we'll provide it if there's a demand for it,
but I'm not sure how useful getting the HANDLE for an NPF device is
(what can you do with it?).

[skip ci]
diff --git a/pcap.c b/pcap.c
index 5fa0e87..0625e66 100644
--- a/pcap.c
+++ b/pcap.c
@@ -3474,8 +3474,11 @@
 		/*
 		 * This is a bogus and now-deprecated API; we
 		 * squelch the narrowing warning for the cast
-		 * from HANDLE to DWORD - Windows programmers
-		 * should use pcap_handle().
+		 * from HANDLE to DWORD.  If Windows programmmers
+		 * need to get at the HANDLE for a pcap_t, *if*
+		 * there is one, they should request such a
+		 * routine (and be prepared for it to return
+		 * INVALID_HANDLE_VALUE).
 		 */
 DIAG_OFF_NARROWING
 		return ((int)(DWORD)p->handle);