esp32/boards/GENERIC_OTA: Enable silent checks to reduce firmware size.

Enabling mDNS put this firmware over the limit of the OTA partition size,
so tweak the compiler settings to reduce the firmware size.

Signed-off-by: Damien George <damien@micropython.org>
diff --git a/ports/esp32/boards/GENERIC_OTA/sdkconfig.board b/ports/esp32/boards/GENERIC_OTA/sdkconfig.board
index d314860..7ff939a 100644
--- a/ports/esp32/boards/GENERIC_OTA/sdkconfig.board
+++ b/ports/esp32/boards/GENERIC_OTA/sdkconfig.board
@@ -1,3 +1,6 @@
 CONFIG_BOOTLOADER_APP_ROLLBACK_ENABLE=y
 CONFIG_PARTITION_TABLE_CUSTOM=y
 CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="partitions-ota.csv"
+
+# Reduce firmware size to fit in the OTA partition.
+CONFIG_COMPILER_OPTIMIZATION_CHECKS_SILENT=y