package/net-tools: fix static linking issue with lintl

package/net-tools: fix static linking issue with lintl

When net-tools are build with uClibc-ng and statically linked,
some tools like hostname and route needs to link with -lintl.

Adding -lintl in LDFLAGS place the library before object files:
arm-linux-gcc -O2 -g -Wall -fno-strict-aliasing   -static -lintl -Llib -o hostname hostname.o

Add $(LIBS) after object files in the Makefile to place -lintl correctly.

Rework NET_TOOLS_BUILD_CMDS to set LDFLAGS with only TARGET_LDFLAGS and
set LIBS with -lintl when needed.

Fixes:
http://autobuild.buildroot.net/results/134/1345b6d366125320b89512e7ce7f142f1a03acf8

Ref:
http://lists.busybox.net/pipermail/buildroot/2016-May/162216.html

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>