dpif-netdev: Modify code comments for function parse_tcp_flags. #2592

Job	Run time
osx clang --disable-ssl	1m 31s
linux deb no dpdk	6m 52s
linux deb shared dpdk	8m 11s
linux gcc --disable-ssl	2m 4s
linux clang --disable-ssl	2m 4s
linux gcc c99	1m 58s
linux clang c99	2m 15s
linux gcc test	7m 14s
linux clang test asan	12m 16s
linux clang test ubsan	9m 3s
linux gcc test --enable-shared	9m 56s
linux clang test --enable-shared	10m 23s
linux gcc test dpdk	14m 15s
linux clang test dpdk	14m 39s
linux gcc test -ljemalloc	7m 32s
linux clang test -ljemalloc	7m 44s
linux gcc afxdp 5.4	2m 49s
linux clang afxdp 5.4	2m 59s
linux gcc dpdk --enable-shared	9m 41s
linux clang dpdk --enable-shared	9m 35s
linux gcc dpdk-shared	8m 44s
linux clang dpdk-shared	8m 42s
linux gcc dpdk-shared --enable-shared	9m 11s
linux clang dpdk-shared --enable-shared	9m 21s
linux gcc m32 --disable-ssl	2m 12s
	3h 1m 11s

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