Reapply "sbin/ping: allow normal users to specify larger packets"

The ping tests were originally broken by an unrelated isue that
is now fixed ( 2926c2594249f64fecbbdcb0b0b9a3591931ab04 ).

THanks to kp@ for fixing the test and Jose Luis Duran for pinting it out.

This reverts commit 7bc0cb91a2dfc7e23d96efd0fb7866ee2a23ba88.