bpf: Use kmalloc_nolock() in bpf streams

bpf: Use kmalloc_nolock() in bpf streams

BPF stream kfuncs need to be non-sleeping as they can be called from
programs running in any context, this requires a way to allocate memory
from any context. Currently, this is done by a custom per-CPU NMI-safe
bump allocation mechanism, backed by alloc_pages_nolock() and
free_pages_nolock() primitives.

As kmalloc_nolock() and kfree_nolock() primitives are available now, the
custom allocator can be removed in favor of these.

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20251023161448.4263-1-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>