libc: convert __dns.c to __dns.cc

Also convert it's header and change it's caller includes.

This patch is done so the libc resolver will be able to retrieve the dns from
OSv dns API.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>
libc: add setter and getter functions for nameservers and search domains

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>
dhcp: wire dhcp dns servers with the libc DNS resolver code.

This Close issue #8 ""Make Java InetAddress.getHostName() works".

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>