autoreconf may need gettext

E. g. for AC_LIB_PREFIX

(cherry picked from commit d57927748a9298780370a66ccb649992cb162646)
Strongswan: use full path to ipsec

This fixes issue:

... charon[6135]: 11[CHD] updown: /bin/sh: ipsec: command not found

(cherry picked from commit 9bbe674927a307f02d32834c9a39f49c8be476e7)
Strongswan: updown script uses ip and iptables utilities

(cherry picked from commit 2b91b9b5941d9ef31ab4e0772ffa03c023abd2cc)
Strongswan: preserve PATH

(cherry picked from commit 17d8029150b246d9cd67174120900ea6bdbedda4)