samples: wifi: shell: Fix regression in performance

Default libc is now picolib and it introduced performance regression in
Zperf, enable speed optimizations to fix the performance regression.

Fixes SHEL-2656.

Signed-off-by: Chaitanya Tata <[email protected]>

Author: krish2718

samples/wifi/shell/overlay-zperf.conf

@@ -10,7 +10,9 @@ CONFIG_NET_BUF_TX_COUNT=60
 CONFIG_HEAP_MEM_POOL_SIZE=230000
 CONFIG_NET_BUF_DATA_SIZE=1100
 CONFIG_NRF700X_QSPI_LOW_POWER=n
-#CONFIG_SPEED_OPTIMIZATIONS=y
+# To enable optimization configuration options
+CONFIG_PICOLIBC_USE_MODULE=y
+CONFIG_SPEED_OPTIMIZATIONS=y
 
 # Necessary for zperf_tcp_receiver.c
 CONFIG_NET_CONFIG_SETTINGS=y