add iscsi_force_reconnect()

If a connection attempt is hung, then iscsi_reconnect() won't do anything. This
makes sense if we'd just re-try to connect to the same target, but if (for
example) login redirect might point us to a different, healthy, target, it
should be possible to restart the full connection process on request.

Signed-off-by: John Levon <john.levon@nutanix.com>

lib/libiscsi.syms.in

@@ -13,6 +13,8 @@ iscsi_discovery_sync
 iscsi_extended_copy_sync
 iscsi_extended_copy_task
 iscsi_free_discovery_data
+iscsi_force_reconnect
+iscsi_force_reconnect_sync
 iscsi_full_connect_async
 iscsi_full_connect_sync
 iscsi_get_error