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).

PR:	151023


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271910 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f