explicitly load kernel-netlink plugin in UML scenarios

testing/tests/sql/ip-pool-db/hosts/carol/etc/strongswan.conf

@@ -6,5 +6,5 @@ charon {
       database = sqlite:///etc/ipsec.d/ipsec.db 
     }
   }
-  load = curl aes des sha1 sha2 md5 gmp random x509 pubkey hmac xcbc stroke sqlite sql
+  load = curl aes des sha1 sha2 md5 gmp random x509 pubkey hmac xcbc stroke kernel-netlink sqlite sql
 }