apps/bttester: Fix build with EATT enabled

EATT support requires at least same number of COC channels.
diff --git a/apps/bttester/syscfg.yml b/apps/bttester/syscfg.yml
index f3352b8..bb4d6f7 100644
--- a/apps/bttester/syscfg.yml
+++ b/apps/bttester/syscfg.yml
@@ -114,7 +114,7 @@
     RTT_NUM_BUFFERS_UP: 0
     RTT_NUM_BUFFERS_DOWN: 0
 
-    BLE_L2CAP_COC_MAX_NUM: 3
+    BLE_L2CAP_COC_MAX_NUM: 5
     BLE_L2CAP_SIG_MAX_PROCS: 2
     BLE_L2CAP_ENHANCED_COC: 1
     BLE_EATT_CHAN_NUM: 5