'vlan_bitmap' is a bitmap and is used as such. So allocate it with
devm_bitmap_zalloc() and its explicit bit size (i.e. VLAN_N_VID).

This avoids the need of the VLAN_BITMAP_SIZE macro which:
   - needlessly has a 'nic_dev' parameter
   - should be "long" (and not byte) aligned, so that the bitmap semantic
     is respected

This is in fact not an issue because VLAN_N_VID is 4096 at the time
being, but devm_bitmap_zalloc() is less verbose and easier to understand.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/6ff7b7d21414240794a77dc2456914412718a145.1656260842.git.christophe.jaillet@wanadoo.frSigned-off-by: Jakub Kicinski <kuba@kernel.org>