tc-testing: fix eBPF tests failure on linux fresh clones

tc-testing: fix eBPF tests failure on linux fresh clones

commit 7145fcfffef1fad4266aaf5ca96727696916edb7 upstream.

when the following command is done on a fresh clone of the kernel tree,

 [root@f31 tc-testing]# ./tdc.py -c bpf

test cases that need to build the eBPF sample program fail systematically,
because 'buildebpfPlugin' is unable to install the kernel headers (i.e, the
'khdr' target fails). Pass the correct environment to 'make', in place of
ENVIR, to allow running these tests.

Fixes: 4c2d39bd40c1 ("tc-testing: use a plugin to build eBPF program")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>