MEDIUM: dns: don't call connect to dest socket for AF_INET*

MEDIUM: dns: don't call connect to dest socket for AF_INET*

When we perform connect call for a datagram socket, used to send DNS requests,
we set for it the default destination address to some given nameserver. Then we
simply use send(), as the destination address is already set. In some usecases
described in GitHub issues #3001 and #2654, this approach becames inefficient,
nameservers change its IP addresses dynamically, this triggers DNS resolution
errors.

To fix this, let's perform the bind() on the wildcard address for the datagram
AF_INET* client socket. Like this we will allocate a port for it. Then let's
use sendto() instead of send().

If the nameserver is local and is listening on the UNIX domain socket, we
continue to use the existed approach (connect() and then send()).

This fixes issues #3001 and #2654.
This may be backported in all stable versions.

(cherry picked from commit 2c7e05f80e3b4bacad84eb213b9db3bc5d8963dc)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit bfcaf34de91339de70ec9556d3c10abb426336e0)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>