C-g cannot stop it. I have left it running for > 15 minutes and no sign
of stopping too.

I know it is gnutls-boot because, I tried:

 - kill -USR2 <pid>
 - killall emacs

and a debug buffer pops up to say that. Unfortunately I was just about
to get a copy of the backtrace and the network was back to normal. But I
think gnutls is doing some funny business. gnutls should kill itself
after some time instead of freeze emacs forever.

Leo