if_vlan: do not enable LRO for bridge interaces

If the parent interface is not a bridge and can do LRO and
checksum offloading on VLANs, then guess it may do LRO on VLANs.
False positive here cost nothing, while false negative may lead
to some confusions. According to Wikipedia:

"LRO should not operate on machines acting as routers, as it breaks
the end-to-end principle and can significantly impact performance."

The same reasoning applies to machines acting as bridges.

PR: 254596
MFC after: 3 weeks