tests: Explicitly store hex IPv6 PD prefix. #4778

Job	Run time
linux rpm fedora	6m 59s
osx clang --disable-ssl	2m 44s
Prepare container	3m 18s
linux gcc --disable-ssl	2m 34s
linux clang --disable-ssl	2m 51s
linux gcc test -300	9m 23s
linux gcc test 301-600	6m 34s
linux gcc test 601- unstable	6m 34s
linux clang test sanitizers -300	12m 49s
linux clang test sanitizers 301-600	9m 14s
linux clang test sanitizers 601- unstable	11m 40s
linux gcc test -ljemalloc -300	10m 6s
linux gcc test -ljemalloc 301-600	6m 44s
linux gcc test -ljemalloc 601- unstable	6m 54s
linux gcc system-test-dpdk dpdk -100	16m 47s
linux gcc system-test-dpdk dpdk 101- unstable	14m 48s
linux gcc system-test-userspace -100	15m 45s
linux gcc system-test-userspace 101- unstable	13m 48s
linux gcc system-test -100	18m 33s
linux gcc system-test 101- unstable	18m 13s
linux clang system-test sanitizers -100	20m 17s
linux clang system-test sanitizers 101- unstable	20m 7s
linux x86 gcc --disable-ssl	2m 43s
	3h 59m 25s

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