iscsi-target: Explicily clear login response PDU in exception path

This patch adds a explicit memset to the login response PDU
exception path in iscsit_tx_login_rsp().

This addresses a regression bug introduced in commit baa4d64
where the initiator would end up not receiving the login
response and associated status class + detail, before closing
the login connection.

Reported-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Tested-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target_util.c

@@ -1295,6 +1295,8 @@ int iscsit_tx_login_rsp(struct iscsi_conn *conn, u8 status_class, u8 status_deta
 	login->login_failed = 1;
 	iscsit_collect_login_stats(conn, status_class, status_detail);
 
+	memset(&login->rsp[0], 0, ISCSI_HDR_LEN);
+
 	hdr	= (struct iscsi_login_rsp *)&login->rsp[0];
 	hdr->opcode		= ISCSI_OP_LOGIN_RSP;
 	hdr->status_class	= status_class;