controller: Avoid quadratic complexity for multi-chassis ports. #1344

Job	Run time
osx clang --disable-ssl	1m 52s
linux rpm fedora	7m 4s
Prepare container	3m 34s
linux gcc --disable-ssl	2m 38s
linux clang --disable-ssl	2m 41s
linux gcc test -300	9m 15s
linux gcc test 301-600	6m 14s
linux gcc test 601- unstable	6m 55s
linux clang test sanitizers -300	12m 24s
linux clang test sanitizers 301-600	9m 6s
linux clang test sanitizers 601- unstable	10m 42s
linux gcc test -ljemalloc -300	9m 35s
linux gcc test -ljemalloc 301-600	6m 34s
linux gcc test -ljemalloc 601- unstable	6m 48s
linux gcc system-test-dpdk dpdk -100	16m 57s
linux gcc system-test-dpdk dpdk 101- unstable	14m 10s
linux gcc system-test-userspace -100	15m 52s
linux gcc system-test-userspace 101- unstable	13m 8s
linux gcc system-test -100	18m 30s
linux gcc system-test 101- unstable	16m 48s
linux clang system-test sanitizers -100	20m 11s
linux clang system-test sanitizers 101- unstable	18m 26s
linux x86 gcc --disable-ssl	2m 39s
	3h 52m 3s

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