northd: Use proper field for lookup_nd #2606

Job	Run time
osx clang --disable-ssl	5m 5s
linux gcc --disable-ssl	2m 25s
linux clang --disable-ssl	2m 21s
linux gcc test -500	11m 51s
linux gcc test 501-1000	8m 10s
linux gcc test 1001-	4m 44s
linux clang test sanitizers -300	9m 49s
linux clang test sanitizers 301-600	11m 27s
linux clang test sanitizers 601-900	7m 3s
linux clang test sanitizers 901-1200	7m 33s
linux clang test sanitizers 1201-	4m 39s
linux gcc test -ljemalloc -500	12m 33s
linux gcc test -ljemalloc 501-1000	8m 12s
linux gcc test -ljemalloc 1001-	4m 52s
linux clang test -ljemalloc -500	13m 13s
linux clang test -ljemalloc 501-1000	8m 35s
linux clang test -ljemalloc 1001-	5m 38s
linux gcc system-test -100	11m 6s
linux gcc system-test 101-200	15m 54s
linux gcc system-test 201-	15m 51s
linux clang system-test sanitizers -100	12m 5s
linux clang system-test sanitizers 101-200	16m 56s
linux clang system-test sanitizers 201-	18m 57s
linux gcc m32 --disable-ssl	2m 9s
	3h 41m 8s

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