When building with strongswan-ipsec disabled, strongswan fails to build
because the ipsec.conf file does not exist. Fix this by moving the
ipsec.* files and directories to the strongswan-ipsec package.
Closes#10879 while keeping ipsec.conf to avoid breaking existing
setups, as opposed to #11709.
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>