Makefile: have check target depend on all

Makefile: have check target depend on all

Otherwise it will simply fail immediately from a just-cleaned
workspace:

$ make check -j1
cd testsuite && make && make alltests
echo "Entering iproute2" && cd iproute2 && make configure && cd ..;
Entering iproute2
make -C tools
Makefile:3: ../../config.mk: No such file or directory
make[2]: *** No rule to make target '../../config.mk'.  Stop.

Fixes: 8804a8c0d387 ("Makefile: Add check target")
Signed-off-by: Luca Boccassi <bluca@debian.org>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Tested-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>