northd: introduce ls_datapath_group column in lb sb db table #1613

Job	Run time
dpdk gcc	7s
linux rpm fedora	12m 50s
osx clang --disable-ssl	6m 8s
linux gcc --disable-ssl	3m 10s
linux clang --disable-ssl	3m 37s
linux gcc test -500	20m 20s
linux gcc test 501-1000	12m 49s
linux gcc test 1001-	6m 58s
linux clang test sanitizers -300	16m 1s
linux clang test sanitizers 301-600	24m 41s
linux clang test sanitizers 601-900	13m 45s
linux clang test sanitizers 901-1200	10m 26s
linux clang test sanitizers 1201-	8m 56s
linux gcc test -ljemalloc -500	25m 41s
linux gcc test -ljemalloc 501-1000	13m 16s
linux gcc test -ljemalloc 1001-	8m 52s
linux gcc system-test-dpdk dpdk -100	14m 15s
linux gcc system-test-dpdk dpdk 101-200	18m 6s
linux gcc system-test-dpdk dpdk 201-	21m 54s
linux gcc system-test-userspace -100	10m 41s
linux gcc system-test-userspace 101-200	14m 50s
linux gcc system-test-userspace 201-	21m 48s
linux gcc system-test -100	14m 59s
linux gcc system-test 101-200	18m 9s
linux gcc system-test 201-	43m 57s
linux clang system-test sanitizers -100	15m 55s
linux clang system-test sanitizers 101-200	19m 15s
linux clang system-test sanitizers 201-	29m 22s
linux x86 gcc --disable-ssl	2m 56s
	7h 13m 44s

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