Add code for manipulation with TCP-MD5 keys in the IPsec SA/SP database at FreeBSD systems. Now, BGP MD5 authentication (RFC 2385) keys are handled automatically on both Linux and FreeBSD. Based on patches from Pavel Tvrdik.
Inspired by the patch from Alexander V. Chernikov.
Remove support for historic Linux kernels, merge krt-iface, krt-set and krt-scan stub headers.