ofproto-dpif-mirror: Always revalidate on mirror update. #2457

Job	Run time
dpdk gcc	1m 54s
linux deb no dpdk	4m 58s
osx clang --disable-ssl	1m 30s
linux gcc --disable-ssl	2m 35s
linux clang --disable-ssl	5m 7s
linux gcc c99	1m 52s
linux clang c99	2m 12s
linux gcc test	7m 8s
linux clang test asan	12m 12s
linux clang test ubsan	9m 15s
linux gcc test --enable-shared	9m 53s
linux clang test --enable-shared	9m 58s
linux gcc test dpdk	7m 36s
linux clang test dpdk	7m 25s
linux gcc test -ljemalloc	7m 56s
linux clang test -ljemalloc	7m 48s
linux gcc --enable-afxdp	1m 59s
linux clang --enable-afxdp	2m 8s
linux gcc dpdk --enable-shared	2m 55s
linux clang dpdk --enable-shared	2m 56s
linux gcc dpdk-shared	2m 12s
linux clang dpdk-shared	2m 14s
linux gcc dpdk-shared --enable-shared	2m 52s
linux clang dpdk-shared --enable-shared	2m 57s
linux gcc m32 --disable-ssl	2m 4s
	2h 1m 36s

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