qemu/nic_bonding: Enlarge the timeout value of the case

There are four actions in the case, host to guest, guest to host
and repeat in another thread, for action, the time out is 1000,
but the whole case's timeout value also 1000, which is unreasonable
and cause failure sometimes.

This patch is to solve this bug.
Signed-off-by: NMike Qiu <qiudayu@linux.vnet.ibm.com>

qemu/tests/cfg/nic_bonding.cfg

@@ -5,7 +5,7 @@
     nics += ' nic2 nic3 nic4'
     image_snapshot = yes
     serial_login = yes
-    test_timeout = 1000
+    test_timeout = 4000
     filesize = 4000
     transfer_timeout = 1000
     transfer_type = remote