Why do "arp -a" doesn't show names on -CURRENT?

[Lev Serebryakov]

 On -CURRENT (r334027)  "arp -a" can not resolve addresses to names. DNS
working, as "drill -x" shows:

% arp -a
? (192.168.136.1) at 00:22:4d:9d:e0:97 on ubnt permanent [vlan]
? (192.168.136.2) at f0:9f:c2:f3:3d:b7 on ubnt expires in 1192 seconds
[vlan]
? (94.19.235.70) at 00:22:4d:9d:e0:97 on skynet permanent [vlan]
? (94.19.235.132) at f4:ec:38:e9:2b:ef on skynet expires in 1141 seconds
[vlan]
? (94.19.234.111) at 28:28:5d:c7:3b:cb on skynet expires in 1186 seconds
[vlan]
? (94.19.224.1) at 00:22:0d:03:d4:00 on skynet expires in 1200 seconds
[vlan]
? (94.19.235.178) at 10:7b:ef:5b:1e:35 on skynet expires in 1197 seconds
[vlan]
? (192.168.135.1) at 00:15:6d:85:5f:fc on wlan0 permanent [ethernet]
? (192.168.134.2) at 0c:c4:7a:90:8d:5e on em0 expires in 1164 seconds
[ethernet]
? (192.168.134.128) at 08:00:27:28:5c:1c on em0 expires in 263 seconds
[ethernet]
? (192.168.134.1) at 00:22:4d:9d:e0:93 on em0 permanent [ethernet]
? (192.168.134.18) at 00:80:a3:91:41:9d on em0 expires in 1190 seconds
[ethernet]
? (192.168.134.16) at 30:5a:3a:e0:93:ef on em0 expires in 639 seconds
[ethernet]

 For example:

% drill -x 192.168.134.18 | grep 18.134.168.192.in-addr.arpa
;; 18.134.168.192.in-addr.arpa. IN      PTR
18.134.168.192.in-addr.arpa.    3079    IN      PTR
sandcat.home.serebryakov.spb.ru.

-- 
// Lev Serebryakov