Now that we no longer depend on the textual IPC format, we can pass IP addresses
in the format most code actually has and needs it: in binary. The only places we
actually have to deal with textual address representation is:
* When reading /etc/hosts, we have to parse textual addresses & convert them to
binary;
* When doing reverse lookups, we have to form a pseudo-hostname of the form
x.x.x.x.in-addr.arpa.
So we do the conversion in those two cases.
This also increases uniformity between how we handle A (IPv4 address) and other
resource record types. Namely, we now store the raw binary data as received from
a DNS server.
The ad-hoc IPC we were doing with LookupServer was kinda gross. With this,
LookupServer is a regular IPC server. In the future, we want to add more APIs
for LookupServer to talk to its clients (such as DHCPClient telling LookupServer
about the DNS server discovered via DHCP, and DNS-SD client browsing for
services), which calls for a more expressive IPC format; this is what LibIPC is
perfect for.
While the LookupServer side is using the regular LibIPC mechanics and patterns,
the LibC side has to hand-roll LibIPC format serialization without actually
using LibIPC. We might be able to get rid of this in the future, but for now it
has to be like that. The good news is the format is not that bad at all.
We were ignoring everything but A records in DNS responses. This broke
reverse lookups which obviously want the PTR records.
Fix this by filtering on the requested record type instead of always A.
