meta-flow: Fix nw_frag mask while parsing from string. #2500

Job	Run time
linux rpm fedora	4m 12s
linux deb no dpdk	7m 25s
osx clang --disable-ssl	1m 46s
dpdk gcc	1m 28s
clang-analyze	17m 44s
linux gcc --disable-ssl	2m 23s
linux clang --disable-ssl	2m 38s
linux gcc c99	2m 24s
linux clang c99	4m 19s
linux gcc test	8m 27s
linux clang address,undefined test	16m 37s
linux gcc test --enable-shared	11m 19s
linux clang test --enable-shared	11m 42s
linux gcc check check-dpdk dpdk	18m 7s
linux clang check check-dpdk dpdk	17m 53s
linux gcc test -ljemalloc	9m 2s
linux clang test -ljemalloc	8m 46s
linux gcc --enable-afxdp	2m 18s
linux clang --enable-afxdp	2m 34s
linux gcc dpdk --enable-shared	3m 30s
linux clang dpdk --enable-shared	3m 23s
linux gcc dpdk-shared	2m 31s
linux clang dpdk-shared	2m 36s
linux gcc dpdk-shared --enable-shared	3m 25s
linux clang dpdk-shared --enable-shared	3m 35s
linux gcc m32 --disable-ssl	2m 42s
linux gcc check-ovsdb-cluster	6m 40s
linux gcc check-kernel -100	8m 51s
linux gcc check-kernel 100-	9m 16s
linux clang address,undefined check-kernel -100	11m 14s
linux clang address,undefined check-kernel 100-	11m 30s
linux gcc check-offloads -100	8m 53s
linux gcc check-offloads 100-	7m 25s
linux gcc dpdk check-system-userspace	11m 1s
linux clang address,undefined dpdk check-system-userspace	14m 48s
linux gcc dpdk check-system-tso	10m 53s
linux gcc dpdk check-afxdp	12m 38s
	4h 45m 55s

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