Modbus: Fix the mbpaHeaderSize typo


Rename it to mbapHeaderSize, matching the MBAP header it sizes.

Pick-to: 6.12 6.11 6.8
Change-Id: I93bf248a026170642e0729944e733a9e8edb4fca
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
commitbe95a9f9129122857bc39a32ae64e65355de86bf
parentbb342e75f7fada924fa69127cd9d0323606c4c90
authorDennis Oberst <dennis.oberst@qt.io>
committerIvan Solovev <ivan.solovev@qt.io>
commit timeMon, 14 Sep 2026 13:23:42 +0000