cifs: Always update signing key of first channel

Update signing key of first channel whenever generating the master
sigining/encryption/decryption keys rather than only in cifs_mount().

This also fixes reconnect when re-establishing smb sessions to other
servers.
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2transport.c

@@ -407,6 +407,10 @@ generate_smb3signingkey(struct cifs_ses *ses,
 				  SMB3_SIGN_KEY_SIZE);
 		if (rc)
 			return rc;
+
+		memcpy(ses->chans[0].signkey, ses->smb3signingkey,
+		       SMB3_SIGN_KEY_SIZE);
+
 		rc = generate_key(ses, ptriplet->encryption.label,
 				  ptriplet->encryption.context,
 				  ses->smb3encryptionkey,