nfs: add server port to rpc_pipe info file

On the client, when an alternate server port is specified on the mount
commandline, we need to make sure gssd knows about it.

Also, on the server side, when we're sending krb5 callbacks to the
client, we'll use the same mechanism to let gssd know about the callback
port.

Thanks to Olga Kornievskaia for testing and for an earlier
implementation.

Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Cc: Olga Kornievskaia <aglo@citi.umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>