libnm-utils: fix typo in bond ad_select bandwidth mode

The correct spelling is `bandwidth` instead of `bandwith`.

https://bugs.launchpad.net/network-manager/+bug/1987001

Fixes: 32870d82 ('libnm-utils: convert string bond opts to int')
56 jobs for ff/fix_bond_typo in 46 minutes and 34 seconds (queued for 4 seconds)
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