ovn-northd.at: Fix flaky VXLAN mode disabling test. #183

Job	Run time
Prepare container	3m 29s
osx clang --disable-ssl	2m 7s
linux rpm fedora	7m 4s
linux gcc --disable-ssl	2m 26s
linux clang --disable-ssl	2m 26s
linux gcc test -300	9m 5s
linux gcc test 301-600	6m 4s
linux gcc test 601- unstable	6m 59s
linux clang test sanitizers -300	12m 12s
linux clang test sanitizers 301-600	8m 36s
linux clang test sanitizers 601- unstable	10m 20s
linux gcc test -ljemalloc -300	9m 30s
linux gcc test -ljemalloc 301-600	6m 12s
linux gcc test -ljemalloc 601- unstable	6m 42s
linux gcc system-test-dpdk dpdk -100	16m 43s
linux gcc system-test-dpdk dpdk 101- unstable	12m 6s
linux gcc system-test-userspace -100	15m 29s
linux gcc system-test-userspace 101- unstable	10m 56s
linux gcc system-test -100	17m 51s
linux gcc system-test 101- unstable	14m 29s
linux clang system-test sanitizers -100	20m 0s
linux clang system-test sanitizers 101- unstable	16m 13s
linux x86 gcc --disable-ssl	2m 24s
	3h 39m 23s

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