samples: wifi: Enable LTO for WIFI sample

Enable LTO for the WIFI shell sample to fix
flash overlfow issue. LTO is experimental but
the same goes for using legacy crypto and PSA
crypto at the same time and this sample does that
as well.

Signed-off-by: Georgios Vasilakis <georgios.vasilakis@nordicsemi.no>

Author: Vge0rge

samples/wifi/shell/overlay-openthread.conf

@@ -31,3 +31,8 @@ CONFIG_LOG_MAX_LEVEL=1
 
 # Consumes more memory
 CONFIG_WIFI_CREDENTIALS=n
+
+# LTO is used here to fix overflowing the flash
+# in this configuration
+CONFIG_LTO=y
+CONFIG_ISR_TABLES_LOCAL_DECLARATION=y