northd: Generate logical router's LB and NAT flows using lr_lbnat_data. #3449

Job	Run time
dpdk gcc	8s
linux rpm fedora	10m 32s
osx clang --disable-ssl	5m 0s
linux gcc --disable-ssl	2m 43s
linux clang --disable-ssl	3m 2s
linux gcc test -300	11m 16s
linux gcc test 301-600	9m 49s
linux gcc test 601-	5m 5s
linux clang test sanitizers -300	21m 7s
linux clang test sanitizers 301-600	14m 4s
linux clang test sanitizers 601-	11m 6s
linux gcc test -ljemalloc -300	14m 12s
linux gcc test -ljemalloc 301-600	8m 9s
linux gcc test -ljemalloc 601-	5m 47s
linux gcc system-test-dpdk dpdk -100	17m 6s
linux gcc system-test-dpdk dpdk 101-	14m 22s
linux gcc system-test-userspace -100	12m 32s
linux gcc system-test-userspace 101-	12m 41s
linux gcc system-test -100	14m 42s
linux gcc system-test 101-	13m 49s
linux clang system-test sanitizers -100	20m 12s
linux clang system-test sanitizers 101-	17m 8s
linux x86 gcc --disable-ssl	2m 44s
	4h 7m 16s

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