ofproto-dpif: Improve load balancing in dp_hash select groups. #2481

Job	Run time
linux rpm fedora	3m 53s
linux deb no dpdk	4m 32s
dpdk gcc	1m 59s
osx clang --disable-ssl	1m 59s
linux gcc --disable-ssl	1m 58s
linux clang --disable-ssl	2m 12s
linux gcc c99	2m 1s
linux clang c99	2m 7s
linux gcc test	7m 31s
linux clang test asan	13m 21s
linux clang test ubsan	9m 12s
linux gcc test --enable-shared	11m 3s
linux clang test --enable-shared	10m 9s
linux gcc test dpdk	8m 59s
linux clang test dpdk	7m 50s
linux gcc test -ljemalloc	7m 52s
linux clang test -ljemalloc	8m 7s
linux gcc --enable-afxdp	2m 3s
linux clang --enable-afxdp	2m 12s
linux gcc dpdk --enable-shared	3m 4s
linux clang dpdk --enable-shared	2m 59s
linux gcc dpdk-shared	2m 24s
linux clang dpdk-shared	2m 24s
linux gcc dpdk-shared --enable-shared	2m 50s
linux clang dpdk-shared --enable-shared	2m 48s
linux gcc m32 --disable-ssl	2m 0s
	2h 7m 29s

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