With libreswan 4 some command line option changed, the rundir is now
/run/pluto instead of /var/run/pluto, and nat_traversal must not be set
in ipsec.conf.
Adapt the libreswan device driver accordingly.
Users will require libreswan v4.0 or higher, compatibility with v3.x is
not maintained.
Closes-Bug: #1938571
Change-Id: Ib55e3c3f9cfbe3dfe1241ace8c821256d7fc174a
55558e8f3b