This patch introduces a new internal response state about the analysis
of a DNS response received by a server.
It is dedicated to report to above layer that the response is
'truncated'.
This patch updates the dns_nameserver structure to integrate a counter
dedicated to 'truncated' response sent by servers.
Such response are important to track, since HAProxy is supposed to
replay its request.
Current DNS client code implementation doesn't take care of response
flags setup by the server.
This patch introduces a couple of bitmasks one can use to retrieve the
truncated flag and the reply code available in the 2-bytes flag field.
3 variables of the dns_resolution structure are set to 'time_t' type.
Since they are all set by 'now_ms' and used as 'ticks' in HAProxy's
internal, it is safer to set them to the same type than now_ms:
'unsigned int'.
Implementation of a DNS client in HAProxy to perform name resolution to
IP addresses.
It relies on the freshly created UDP client to perform the DNS
resolution. For now, all UDP socket calls are performed in the
DNS layer, but this might change later when the protocols are
extended to be more suited to datagram mode.
A new section called 'resolvers' is introduced thanks to this patch. It
is used to describe DNS servers IP address and also many parameters.
