ifupdownaddons: bridgeutils: uncomment parsing code for brctl mc attributes

ifupdownaddons: bridgeutils: uncomment parsing code for brctl mc attributes

Ticket: None
Reviewed By: Roopa, Nikhil G
Testing Done: ssim ifupdown2-tests

runtests.sh -T ~/result_smoke/single/ifupdown2-tests.log -r ~/result_smoke/single/summary_ifupdown2tests.txt -d cel-redxp-06 -t nightly -l INFO -k $VM_BASE_KERNEL -i $VM_BASE_IMG $TESTS_HOME/tests/smoke/testOneConfigifupdown2.py:Testifupdown2OneConfig

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>