linkmode: Change return type of linkmode_andnot to bool

linkmode: Change return type of linkmode_andnot to bool

linkmode_andnot() simply returns the result of bitmap_andnot().
And the return type of bitmap_andnot() is bool.
So it makes sense for the return type of linkmode_andnot()
to also be bool.

I checked all call-sites and they either ignore the return
value or treat it as a bool.

Compile tested only.

Link: https://lore.kernel.org/netdev/68088998-4486-4930-90a4-96a32f08c490@lunn.ch/
Signed-off-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240801-linkfield-bowl-v1-1-d58f68967802@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>