save-keys: Add save-keys plugin

This plugin will export IKE_SA and CHILD_SA secret keys in the format used
by Wireshark.

It has to be loaded explicitly.

src/libcharon/Makefile.am

@@ -208,6 +208,13 @@ if MONOLITHIC
 endif
 endif
 
+if USE_SAVE_KEYS
+ SUBDIRS += plugins/save_keys
+if MONOLITHIC
+ libcharon_la_LIBADD += plugins/save_keys/libstrongswan-save-keys.la
+endif
+endif
+
 if USE_SOCKET_DEFAULT
   SUBDIRS += plugins/socket_default
 if MONOLITHIC