conf, pasta: With --config-net, copy all addresses by default

Use the newly-introduced NL_DUP mode for nl_addr() to copy all the
addresses associated to the template interface in the outer
namespace, unless --no-copy-addrs (also implied by -a) is given.

This option is introduced as deprecated right away: it's not expected
to be of any use, but it's helpful to keep it around for a while to
debug any suspected issue with this change.

This is done mostly for consistency with routes. It might partially
cover the issue at:
  https://bugs.passt.top/show_bug.cgi?id=47
  Support multiple addresses per address family

for some use cases, but not the originally intended one: we'll still
use a single outbound address (unless the routing table specifies
different preferred source addresses depending on the destination),
regardless of the address used in the target namespace.

Link: https://bugs.passt.top/show_bug.cgi?id=47
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

passt.1

@@ -563,6 +563,20 @@ future version. It is not expected to be of any use, and it simply reflects a
 legacy behaviour. If you have any use for this, refer to \fBREPORTING BUGS\fR
 below.
 
+.TP
+.BR \-\-no-copy-addrs " " (DEPRECATED)
+With \-\-config-net, do not copy all the addresses associated to the interface
+we derive addresses and routes from: set up a single one. Implied by \-a,
+\-\-address.
+
+Default is to copy all the addresses, except for link-local ones, from the
+interface from the outer namespace to the target namespace.
+
+Note that this configuration option is \fBdeprecated\fR and will be removed in a
+future version. It is not expected to be of any use, and it simply reflects a
+legacy behaviour. If you have any use for this, refer to \fBREPORTING BUGS\fR
+below.
+
 .TP
 .BR \-\-ns-mac-addr " " \fIaddr
 Configure MAC address \fIaddr\fR on the tap interface in the namespace.