ebtables: move ebtables-save to sbindir to avoid QA issue

Fix the QA issue:
WARNING: QA Issue: ebtables: Found a reference to /usr/ in
    /path/to/tmp/work/x86_64-wrs-linux/ebtables-2.0.10-4-r1/packages-split/ebtables/sbin/ebtables-save
WARNING: QA Issue: Shell scripts in base_bindir and base_sbindir should not reference anything in exec_prefix

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Joe MacDonald <joe.macdonald@windriver.com>