[nrf fromtree] net: wifi: shell: Fix alloc failures during cert validation

Memory allocation failures during certificate validation causes
connection termination. Increase MBEDTLS_HEAP_SIZE to fix this.

Signed-off-by: Ravi Dondaputi <[email protected]>
(cherry picked from commit 58591c6)

Author: rado17

samples/net/wifi/overlay-enterprise.conf

@@ -7,4 +7,4 @@ CONFIG_NET_BUF_RX_COUNT=36
 # For TLS and X.509 processing MbedTLS needs large heap size and using separate heap
 # for MbedTLS gives us more control over the heap size.
 CONFIG_MBEDTLS_ENABLE_HEAP=y
-CONFIG_MBEDTLS_HEAP_SIZE=55000
+CONFIG_MBEDTLS_HEAP_SIZE=60000