use libiconv-tiny as default for uClibc-ng

target/config/Config.in.toolchain

@@ -4,6 +4,7 @@
 choice
 prompt "Iconv implementation"
 bool
+default ADK_TARGET_LIBICONV_TINY if ADK_TARGET_LIB_UCLIBC_NG
 
 config ADK_TARGET_LIBC_ICONV
 	prompt "Use iconv from C library"