northd: Allow announcing individual host routes. #4739

Job	Run time
Prepare container	3m 44s
osx clang --disable-ssl	1m 50s
linux rpm fedora	7m 16s
linux gcc --disable-ssl	2m 46s
linux clang --disable-ssl	2m 44s
linux gcc test -300	9m 25s
linux gcc test 301-600	6m 18s
linux gcc test 601- unstable	6m 44s
linux clang test sanitizers -300	12m 57s
linux clang test sanitizers 301-600	9m 8s
linux clang test sanitizers 601- unstable	11m 48s
linux gcc test -ljemalloc -300	9m 56s
linux gcc test -ljemalloc 301-600	6m 34s
linux gcc test -ljemalloc 601- unstable	6m 51s
linux gcc system-test-dpdk dpdk -100	16m 53s
linux gcc system-test-dpdk dpdk 101- unstable	14m 57s
linux gcc system-test-userspace -100	16m 8s
linux gcc system-test-userspace 101- unstable	13m 45s
linux gcc system-test -100	18m 16s
linux gcc system-test 101- unstable	18m 9s
linux clang system-test sanitizers -100	20m 13s
linux clang system-test sanitizers 101- unstable	20m 9s
linux x86 gcc --disable-ssl	2m 35s
	3h 59m 6s

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