pppoe: drop PFC frames

...

SUSE CVE-2023-53369

In the Linux kernel, the following vulnerability has been resolved: net: dcb: choose correct policy to parse DCBATTRBCN The dcbnlbcnsetcfg uses erroneous policy to parse tbDCBATTRBCN, which is introduced in commit 859ee3c43812 "DCB: Add support for DCB BCN". Please see the comment in below code...