devtools: fix orphan symbols check with busybox
devtools: fix orphan symbols check with busybox

Avoid relying on GNU grep --exclude option.

Fixes: f8ad40dc998c ("devtools: check orphan symbols in map files")
Cc: stable@dpdk.org

Signed-off-by: David Marchand <f28529695cfa9e3e1eb84e7072aa626af4abb18e@redhat.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk