driver:dwmac: Removed failing check for VLAN promisc mode

The commit is a workaround to re-allow the internal mac to be added to a software bridge.

Also see https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/ Workaround-for-issue-Bridge-mode-on-EQoS-module-will-not-work/ta-p/1559302

BCS 746-001292