arping: change a few message strings to be closer to iputils arping

arping: change a few message strings to be closer to iputils arping

ARPING 192.168.1.1 from 192.168.1.172 wlan0
Unicast reply from 192.168.1.1 [F4:F2:6D:52:A8:DE]  1.672ms
Sent 1 probes (1 broadcast(s))
Received 1 response(s)

ARPING 192.168.1.1 from 192.168.1.172 wlan0
Unicast reply from 192.168.1.1 [f4:f2:6d:52:a8:de] 1.152ms
Sent 1 probe(s) (1 broadcast(s))
Received 1 response(s) (0 request(s), 0 broadcast(s))

function                                             old     new   delta
finish                                               120     100     -20

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>