northd: Make sure that we keep explicit chassis for remote PB. #3266

Job	Run time
osx clang --disable-ssl	2m 20s
Prepare container	1m 25s
linux rpm fedora	6m 58s
linux gcc --disable-ssl	2m 54s
linux clang --disable-ssl	2m 58s
linux gcc test -300	9m 19s
linux gcc test 301-600	6m 15s
linux gcc test 601- unstable	7m 26s
linux clang test sanitizers -300	12m 47s
linux clang test sanitizers 301-600	8m 58s
linux clang test sanitizers 601- unstable	11m 13s
linux gcc test -ljemalloc -300	9m 41s
linux gcc test -ljemalloc 301-600	6m 47s
linux gcc test -ljemalloc 601- unstable	7m 2s
linux gcc system-test-dpdk dpdk -100	17m 33s
linux gcc system-test-dpdk dpdk 101- unstable	14m 20s
linux gcc system-test-userspace -100	15m 50s
linux gcc system-test-userspace 101- unstable	13m 16s
linux gcc system-test -100	18m 48s
linux gcc system-test 101- unstable	17m 34s
linux clang system-test sanitizers -100	20m 11s
linux clang system-test sanitizers 101- unstable	19m 26s
linux x86 gcc --disable-ssl	2m 48s
	3h 55m 49s

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