net: mvpp2: prs: Drop unnecessary swab16 in vlan detection

Vlan IDs must not be swapped when creating Header Parser entries. This
has no effect on little-endian systems, but is wrong for big-endian.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>