cifs: dns resolution is needed only for primary channel

BugLink: https://bugs.launchpad.net/bugs/2118807

When calling cifs_reconnect, before the connection to the
server is reestablished, the code today does a DNS resolution and
updates server->dstaddr.

However, this is not necessary for secondary channels. Secondary
channels use the interface list returned by the server to decide
which address to connect to. And that happens after tcon is reconnected
and server interfaces are requested.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>
(cherry picked from commit b4f60a053a2534c3e510ba0c1f8727566adf8317)
Signed-off-by: Vinicius Peixoto <vinicius.peixoto@canonical.com>
Acked-by: Manuel Diewald <manuel.diewald@canonical.com>
Acked-by: Alessio Faina <alessio.faina@canonical.com>
Signed-off-by: Vinicius Peixoto <vinicius.peixoto@canonical.com>

Author: sprasad-microsoft

fs/smb/client/connect.c

@@ -392,7 +392,8 @@ static int __cifs_reconnect(struct TCP_Server_Info *server,
 		try_to_freeze();
 		cifs_server_lock(server);
 
-		if (!cifs_swn_set_server_dstaddr(server)) {
+		if (!cifs_swn_set_server_dstaddr(server) &&
+		    !SERVER_IS_CHAN(server)) {
 			/* resolve the hostname again to make sure that IP address is up-to-date */
 			rc = reconn_set_ipaddr_from_hostname(server);
 			cifs_dbg(FYI, "%s: reconn_set_ipaddr_from_hostname: rc=%d\n", __func__, rc);