northd: Fix action parsing in build_lb_vip_actions(). #3450

Job	Run time
dpdk gcc	3s
linux rpm fedora	6m 35s
osx clang --disable-ssl	2m 5s
Prepare container	2m 1s
linux gcc --disable-ssl	2m 6s
linux clang --disable-ssl	2m 17s
linux gcc test -300	9m 5s
linux gcc test 301-600	6m 13s
linux gcc test 601- unstable	5m 59s
linux clang test sanitizers -300	12m 5s
linux clang test sanitizers 301-600	8m 35s
linux clang test sanitizers 601- unstable	9m 37s
linux gcc test -ljemalloc -300	9m 38s
linux gcc test -ljemalloc 301-600	6m 39s
linux gcc test -ljemalloc 601- unstable	6m 19s
linux gcc system-test-dpdk dpdk -100	15m 26s
linux gcc system-test-dpdk dpdk 101- unstable	11m 27s
linux gcc system-test-userspace -100	14m 36s
linux gcc system-test-userspace 101- unstable	10m 27s
linux gcc system-test -100	19m 30s
linux gcc system-test 101- unstable	16m 34s
linux clang system-test sanitizers -100	21m 20s
linux clang system-test sanitizers 101- unstable	18m 11s
linux x86 gcc --disable-ssl	2m 9s
	3h 38m 57s

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