Documentation/isdn: check and fix dead links ...

and switch to https where possible.

All links have been eyeballed to verify that the domains have
not changed, etc.

Signed-off-by: Sanjeev Gupta <ghane0@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/Documentation/isdn/INTERFACE.CAPI b/Documentation/isdn/INTERFACE.CAPI
index 1688b5a..021aa9c 100644
--- a/Documentation/isdn/INTERFACE.CAPI
+++ b/Documentation/isdn/INTERFACE.CAPI
@@ -18,7 +18,7 @@
 directions between the application and the hardware driver.
 
 Format and semantics of CAPI messages are specified in the CAPI 2.0 standard.
-This standard is freely available from http://www.capi.org.
+This standard is freely available from https://www.capi.org.
 
 
 2. Driver and Device Registration