oping: Add the "-m <mark>" command line option.
oping: Add the "-m <mark>" command line option.

This exposes the new "MARK" functionatlity to command line users.

barak/liboping,barak/liboping,iseki-masaya/liboping,octo/liboping,octo/liboping,iseki-masaya/liboping,iseki-masaya/liboping,octo/liboping,barak/liboping,octo/liboping,iseki-masaya/liboping