slirp: Remove our_addr code

Three problems with our_addr:

- It's determined only once when qemu starts, but the address can change
(just like the DNS configuration can).

- It's supposed to be the IP address of a host network interface, but
there's no guarantee that gethostbyname(gethostname()) actually does
that: the host might be a laptop that has only a loopback interface up,
or the hostname might be localhost.localdomain, etc.

- It's useless at best: get_dns_addr() calls it, there's no reason to
send DNS requests to a different IP address if you're running a DNS
server on the host and resolv.conf points to 127.0.0.1.

These problems are easily solved by removing the code.

Signed-off-by: Ed Swierk <eswierk@aristanetworks.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
