rarpd: remove gethostby*() calls

[yanhaowang]

Summary

1. Use getaddrinfo to replace gethostbyname.
2. Update choose_ipaddr() function to take a more general parameter. Use struct addrinfo pointer as address list.

Test Plan

I use "nemesis" pkg to simulate rarp packet and use "tcpdump" to capture the send and response rarp packet and it seem work fine.

1. Add a simulate MAC on "/etc/ethers" and add hosts.

$ cat /etc/ethers 
00:0c:29:02:ba:a1 mytesthost

$ cat /etc/hosts
192.168.42.128 mytesthost

2. Then simulate with "nemesis" like below output. I also add some output about choose_ipaddr function to see if it output same as before.

// Same output on both revsied and not revised code
$ sudo rarpd -a -f -s
IP address: 192.168.42.128

$ sudo nemesis arp -d le0 -S 192.168.42.128 -D 192.168.42.255 -h 00:0c:29:02:ba:a1 -m 00:0c:29:02:ba:a1 -R

$ sudo tcpdump -i le0 ether proto 0x8035 -vvv
tcpdump: listening on le0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
11:25:58.921947 ARP, Ethernet (len 6), IPv4 (len 4), Reverse Request who-is mytesthost tell mytesthost, length 28
11:25:58.922065 ARP, Ethernet (len 6), IPv4 (len 4), Reverse Reply mytesthost at mytesthost, length 28

[yanhaowang]

Fix file permission.

[yanhaowang]

Fix return value error