BandwidthController - fix bugprone-suspicious-missing-comma warnings

Fixes:
  system/netd/server/BandwidthController.cpp:230:13: warning: suspicious string literal, probably missing a comma [bugprone-suspicious-missing-comma]

(and fixing that reveals more that I'm also fixing)

Note: Using parenthesis seems better than marking with
  // NOLINTNEXTLINE(bugprone-suspicious-missing-comma)

Test: builds
Bug: 153035880
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I95d3b1cda93e5a55504e6cd94a795e259863d47f