strongswan: Update to 5.6.2

strongswan: Update to 5.6.2

Fixed a DoS vulnerability in the parser for PKCS#1 RSASSA-PSS
signatures that was caused by insufficient input validation.
One of the configurable parameters in algorithm identifier
structures for RSASSA-PSS signatures is the mask generation
function (MGF). Only MGF1 is currently specified for this purpose.
However, this in turn takes itself a parameter that specifies
the underlying hash function. strongSwan's parser did not
correctly handle the case of this parameter being absent,
causing an undefined data read.

This vulnerability has been registered as CVE-2018-6459.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>