Made some options connection-entry specific

Made some options connection-entry specific

The following options may now be used in a connection block:

 fragment
 mssfix
 tun-mtu
 tun-mtu-extra
 link-mtu
 mtu_discover_type
 explicit-exit-notification

In order to support stuff like
<connection>
  remote host
  proto udp
  fragment
  explicit-exit-notification 3
</connection>
<connection>
  remote host
  proto tcp
</connection>

Signed-off-by: Jan Just Keijser <janjust@nikhef.nl>
Acked-by: David Sommerseth <davids@redhat.com>
Signed-off-by: David Sommerseth <davids@redhat.com>