Merge branch 'netlink-extensions'

Merge branch 'netlink-extensions'

Introduces options to enable concurrent Netlink queries. While this does not
make much sense on vanilla Linux, this can help on third party stacks to
increase throughput if longer latencies are to expect. Netlink message
retransmission can be optionally enabled if transmission is unreliable.
Non-socket based IKE bypass policies and other tweaks bring better compatibility
to third party stacks using Netlink.