ipsec: T1210: extend remote-access smoketest with IP pool configuration

This extends commit 1a84c4d0e ("ipsec: T1210: add smoketest for remote-access
(road-warrior) users") in a way that also the IPv4 pool and its DNS servers get
validated. There is no separate IPv6 test, as both address families behave
the same way when configuring these.