Create a branch for integrating changes needed for netdump.

netdump is a facility that allows the kernel to transmit a kernel dump
over UDP to a remote server, instead of saving it to local media. This
is useful for diskless systems and for centralized collection of kernel
dumps in a lab environment.

This implementation will provide a kernel netdump client, including
hooks for some NIC drivers, and support for configuration with
dumpon(8). Some extensions to the mbuf allocator make it possible to
allocate mbufs/clusters after a panic using a pre-allocated pool;
this is done without imposing any runtime overhead in the regular
allocator and without having to modify driver tx/rx code. The netdump
server component is available in the ports tree as ftp/netdumpd.