For STP to work, receiving BPDUs is essential, but the appropriate bit
was never set. Without GC_RX_BPDU_EN, the switch chip will filter all
BPDUs, even if an appropriate PVID VLAN was setup.
Fixes: ff39c2d68679 ("net: dsa: b53: Add bridge support")
Signed-off-by: Jonas Gorski <jonas.gorski@xxxxxxxxx>