doc/netlink: Add delete operation to ovs_vport spec

Add del operation to the spec to help with testing.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20230824142221.71339-1-donald.hunter@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>