Bring DPDK route lookups to FreeBSD.

This change introduces loadable fib lookup modules based on
DPDK rte_lpm lib targeted for high-speed lookups in large-scale tables.
It is based on the lookup framework described in D27401.

IPv4 module is called dpdk_lpm4. It wraps around rte_lpm [1] library.
This library implements variation of DIR24-8 [2] lookup algorithm.
Module provide lockless route lookups and in-place incremental updates,
allowing for good RIB performance.

IPv6 module is called dpdk_lpm6. It wraps around rte_lpm6 [3] library.
Implementation can be seen as multi-bit trie where the stride or number of bits
inspected on each level varies from level to level.
It can vary from 1 to 14 memory accesses, with 5 being the average value
for the lengths that are most commonly used in IPv6.
Module provide lockless route lookups for global unicast addresses
and in-place incremental updates, allowing for good RIB performance.

Implementation details:
* wrapper code lives in `sys/contrib/dpdk_rte_lpm/dpdk_lpm[6].c`.
* rte_lpm[6] implementation contains both RIB and FIB code.
. RIB ("rule_") code, backed by array of hash tables part has been commented out,
as base radix already provides all the necessary primitives.
* link-local lookups are currently implemented as base radix lookup.
This part should be converted to something like read-only radix trie.

Usage detail:
Compile kernel with option FIB_ALGO and load dpdk_lpm4/dpdk_lpm6
module at any time. They will be picked up automatically when
amount of routes raises to several thousand.

[1]: https://doc.dpdk.org/guides/prog_guide/lpm_lib.html
[2]: http://yuba.stanford.edu/~nickm/papers/Infocom98_lookup.pdf
[3]: https://doc.dpdk.org/guides/prog_guide/lpm6_lib.html

Differential Revision: https://reviews.freebsd.org/D27412