*improve SSE4.1 optimizations of class SynetConvolution16bNhwcDepthwise. #642

Job	Run time
build_and_test_clang (Debug)	14m 56s
build_and_test_gcc_old (10, Debug)	14m 22s
build_and_test_gcc_new (13, Debug)	16m 24s
build_and_test_clang (Release)	16m 1s
build_and_test_gcc_old (10, Release)	16m 8s
build_aarch64_cross (Debug)	3m 53s
build_and_test_gcc_new (13, Release)	19m 53s
build_and_test_gcc_old (11, Debug)	14m 25s
build_aarch64_cross (Release)	4m 8s
build_and_test_mingw (Debug)	18m 32s
build_and_test_gcc_old (11, Release)	16m 23s
build_and_test_mingw (Release)	17m 16s
build_arm_cross (Debug)	4m 34s
build_arm_cross (Release)	3m 28s
	3h 0m 23s

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