10427 in.ndpd does not need to run if only loopback IPv6 addresses are present

Upstream of part of Joyent's OS-1159

Work by Jerry Jelinek


root@hawkeye:~# ipadm show-addr
ADDROBJ           TYPE     STATE        ADDR
lo0/v4            static   ok           127.0.0.1/8
net0/_a           from-gz  ok           10.0.0.86/26
lo0/v6            static   ok           ::1/128

root@hawkeye:~# ps -ef | grep ndpd
    root  4960  4302   0   Jan 22 ?           0:00 /usr/lib/inet/in.ndpd


and post this change, in.ndpd is not started if there is just a loopback IPv6 address.