northd: Prevent assert with wrong LSP configuration. #3441

# to view logs

Job	Run time
linux rpm fedora	6m 42s
osx clang --disable-ssl	2m 11s
Prepare container	3m 14s
linux gcc --disable-ssl	2m 33s
linux clang --disable-ssl	2m 51s
linux gcc test -300	9m 31s
linux gcc test 301-600	6m 57s
linux gcc test 601- unstable	6m 26s
linux clang test sanitizers -300	12m 36s
linux clang test sanitizers 301-600	9m 32s
linux clang test sanitizers 601- unstable	10m 32s
linux gcc test -ljemalloc -300	10m 8s
linux gcc test -ljemalloc 301-600	7m 3s
linux gcc test -ljemalloc 601- unstable	6m 40s
linux gcc system-test-dpdk dpdk -100	16m 15s
linux gcc system-test-dpdk dpdk 101- unstable	13m 58s
linux gcc system-test-userspace -100	15m 24s
linux gcc system-test-userspace 101- unstable	12m 51s
linux gcc system-test -100	20m 9s
linux gcc system-test 101- unstable	19m 52s
linux clang system-test sanitizers -100	22m 3s
linux clang system-test sanitizers 101- unstable	21m 59s
linux x86 gcc --disable-ssl	2m 40s
	4h 2m 7s

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