oxnas: build with 8021Q VLAN support

CONFIG_VLAN_8021Q was explicitely disabled in oxnas kernel config.
Don't do that, so VLANs can be used on the target.

Fixes: dcc34574ef ("oxnas: bring in new oxnas target")
Signed-off-by: Daniel Golle <[email protected]>

target/linux/oxnas/config-5.4

@@ -350,7 +350,6 @@ CONFIG_VERSATILE_FPGA_IRQ=y
 CONFIG_VERSATILE_FPGA_IRQ_NR=4
 CONFIG_VFAT_FS=y
 # CONFIG_VFP is not set
-# CONFIG_VLAN_8021Q is not set
 CONFIG_VM_EVENT_COUNTERS=y
 # CONFIG_WATCHDOG is not set
 # CONFIG_WQ_POWER_EFFICIENT_DEFAULT is not set