iscsi-target: Bump default TCP listen backlog to 256

This patch bumps the default TCP listen backlog within iscsit_setup_np()
from 5 to 256, in order to reduce the overall latency caused by a small
backlog with 100's of simultaneous login attempts directed to the same
single network portal.

Also add a ISCSIT_TCP_BACKLOG macro in iscsi_target_core.h.
Signed-off-by: NNicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target_core.h

@@ -19,6 +19,7 @@
 #define WHITE_SPACE			" \t\v\f\n\r"
 #define ISCSIT_MIN_TAGS			16
 #define ISCSIT_EXTRA_TAGS		8
+#define ISCSIT_TCP_BACKLOG		256
 
 /* struct iscsi_node_attrib sanity values */
 #define NA_DATAOUT_TIMEOUT		3

drivers/target/iscsi/iscsi_target_login.c

@@ -873,7 +873,7 @@ int iscsit_setup_np(
 	struct __kernel_sockaddr_storage *sockaddr)
 {
 	struct socket *sock = NULL;
-	int backlog = 5, ret, opt = 0, len;
+	int backlog = ISCSIT_TCP_BACKLOG, ret, opt = 0, len;
 
 	switch (np->np_network_transport) {
 	case ISCSI_TCP: