geth: add libiconv-full dependency if build with NLS

Variable ICONV_DEPENDS is specified in nls.mk which can be found in
OpenWrt main repository.

This fixes issue:
/foo/build/staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-8.4.0_musl_eabi/lib/gcc/arm-openwrt-linux-muslgnueabi/8.4.0/../../../../arm-openwrt-linux-muslgnueabi/bin/ld: cannot find -liconv

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>

net/geth/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=go-ethereum
 PKG_VERSION:=1.9.22
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://codeload.github.com/ethereum/go-ethereum/tar.gz/v${PKG_VERSION}?
@@ -35,7 +35,7 @@ define Package/geth
   CATEGORY:=Network
   TITLE:=Ethereum Go client
   URL:=https://geth.ethereum.org/
-  DEPENDS:=$(GO_ARCH_DEPENDS)
+  DEPENDS:=$(GO_ARCH_DEPENDS) $(ICONV_DEPENDS)
 endef
 
 define Package/geth/description