Reordering ping parameters to work with AIX.

For GNU/Linux (at least RHEL 6), the ping parameters order doesn't
matter. But for AIX I get an error with the original order:

$ sudo ping -n 127.0.0.1 -w 3 -c 2
0821-077 ping: illegal packet size.

and it works if the parameters order just get rearranged:

$ sudo ping -w 3 -c 2 -n 127.0.0.1
PING 127.0.0.1: (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=0 ms
64 bytes from 127.0.0.1: icmp_seq=1 ttl=255 time=0 ms

--- 127.0.0.1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0/0/0 ms
Merge pull request #79 from ttres/master

Reordering ping parameters to work with AIX.