qca-wifi: Set threshold for WMI diag event queue length

Limit DIAG queue length to avoid memory lockup.

In use-cases where all the cores are busy executing interrupt
handlers and tasklets, work/processes might starve.

To avoid memory being locked up in wmi buf queue which is processed
in work ctxt, it is essential to limit the queue length.

Since highest proportion of the WMI events processed in work ctxt
are FW diag events, to avoid memory lock up, drop FW diag events
when queue length threshold is reached.

Change-Id: I1982eff5bea6b49c0e0b0987c439d2b7af04922e
CRs-Fixed: 2785768

configs/wlan_cfg/ap_wlan_cfg.config

@@ -41,3 +41,4 @@ endif
 
 EXTRA_CFLAGS += -DWLAN_PSOC_MAX_VDEVS=60
 EXTRA_CFLAGS += -DWLAN_PDEV_MAX_VDEVS=30
+EXTRA_CFLAGS += -DRX_DIAG_WQ_MAX_SIZE=1000