Setting frag_size to 0 to indicate kmalloc has been deprecated,
use slab_build_skb directly.

Fixes: ce098da1 ("skbuff: Introduce slab_build_skb()")
Signed-off-by: Aryan Srivastava <aryan.srivastava@alliedtelesis.co.nz>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/r/20240613024900.3842238-1-aryan.srivastava@alliedtelesis.co.nzSigned-off-by: Jakub Kicinski <kuba@kernel.org>