Add -x waittime and -X timeout options for feature parity.  These are
equivalent to -W and -t options of ping(8).  Different letters are used
because both have already been used for another purposes in ping6(8).


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273211 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f