northd: Make sure that we keep explicit chassis for remote PB. #1448

Job	Run time
Prepare container	3m 35s
osx clang --disable-ssl	1m 53s
linux rpm fedora	6m 46s
linux gcc --disable-ssl	2m 51s
linux clang --disable-ssl	2m 39s
linux gcc test -300	9m 26s
linux gcc test 301-600	6m 23s
linux gcc test 601- unstable	6m 29s
linux clang test sanitizers -300	12m 48s
linux clang test sanitizers 301-600	8m 59s
linux clang test sanitizers 601- unstable	11m 28s
linux gcc test -ljemalloc -300	9m 57s
linux gcc test -ljemalloc 301-600	6m 26s
linux gcc test -ljemalloc 601- unstable	6m 44s
linux gcc system-test-dpdk dpdk -100	17m 0s
linux gcc system-test-dpdk dpdk 101- unstable	14m 15s
linux gcc system-test-userspace -100	16m 24s
linux gcc system-test-userspace 101- unstable	13m 24s
linux gcc system-test -100	18m 28s
linux gcc system-test 101- unstable	17m 30s
linux clang system-test sanitizers -100	20m 23s
linux clang system-test sanitizers 101- unstable	19m 6s
linux x86 gcc --disable-ssl	2m 39s
	3h 55m 33s

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