MFC r271910, r273211:

MFC r271910, r273211:

* 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).

* Fix a problem that reply packets are not received when -i T option is set
  and (T < RTT).

 - Use select(2) for timeout instead of interval timer. Remove poll(2) support.
 - Use sigaction(2) instead of signal(3).
 - Exit in SIGINT handler when two signals are received and doing reverse DNS
   lookup as ping(8) does.
 - Remove redundant variables used for getaddrinfo(3).

Approved by:	re (gjb)

git-svn-id: svn://svn.freebsd.org/base/stable/10@285820 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f