Merge branch 'kernel-libipsec'

Merge branch 'kernel-libipsec'

Adds a new kernel interface plugin that uses TUN devices and libipsec to
provide IPsec process in userland.

It works on Linux, FreeBSD and Mac OS X.  In particular the latter two
platforms may gain from this approach as their respective kernels don't
provide support for AES-GCM.

kernel-pfroute has been improved (source address lookup) and a second
plugin (osx-attr) installs configuration attributes (currently DNS
servers only) via SystemConfiguration on Mac OS X.