test/nvmf: increase waitforserial() initial wait time

Increase waitforserial() function initial wait time.
When testing with 5.16.X kernel version 2 seconds were
not enough and issuing a "disconnect" immediatelly after
"connect" caused keepalive timeout.

Fixes #2467

Signed-off-by: Karol Latecki <karol.latecki@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/12587 (master)

(cherry picked from commit dacd8ec827)
Change-Id: Ib913be35b2383daf5f5037e258bbdd2477810921
Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/12649
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>

test/common/autotest_common.sh

@@ -1039,11 +1039,11 @@ function waitforserial() {
 		nvme_device_counter=$2
 	fi
 
-	# Wait initially for min 2s to make sure all devices are ready for use. It seems
+	# Wait initially for min 4s to make sure all devices are ready for use. It seems
 	# that we may be racing with a kernel where in some cases immediate disconnect may
 	# leave dangling subsystem with no-op block devices which can't be used nor removed
 	# (unless kernel is rebooted) and which start to negatively affect all the tests.
-	sleep 2
+	sleep 4
 	while ((i++ <= 15)); do
 		nvme_devices=$(lsblk -l -o NAME,SERIAL | grep -c "$1")
 		((nvme_devices == nvme_device_counter)) && return 0