add module unload support globally, useful for debugging

target/linux/kernel.config

@@ -25,6 +25,7 @@ CONFIG_TMPFS=y
 CONFIG_NLS=y
 CONFIG_EMBEDDED=y
 CONFIG_MODULES=y
+CONFIG_MODULE_UNLOAD=y
 CONFIG_BINFMT_ELF=y
 CONFIG_BINFMT_SCRIPT=y
 CONFIG_HOTPLUG=y