Properly handle EOF condition on libkrad sockets

Properly handle EOF condition on libkrad sockets

In the previous code, when the remote peer performed an orderly shutdown
on the socket, libkrad would enter a state in which all future requests
timed out.  Instead, if the peer shuts down its socket, we need to
attempt to reopen it.

ticket: 8504 (new)
target_version: 1.14-next
tags: pullup