net: sched: codel replace GPLv2/BSD boilerplate

net: sched: codel replace GPLv2/BSD boilerplate

The prologue to codel is using BSD-3 clause and GPL-2 boiler plate
language. Replace it by using SPDX. The automated treewide scan in
commit d2912cb15bdd ("treewide: Replace GPLv2 boilerplate/reference with
SPDX - rule 500") did not pickup dual licensed code.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Dave Taht <dave.taht@gmail.com>
Link: https://lore.kernel.org/r/20240211172532.6568-1-stephen@networkplumber.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>