bpf: Re-enable unit_size checking for global per-cpu allocator

With pcpu_alloc_size() in place, check whether or not the size of
the dynamic per-cpu area is matched with unit_size.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20231020133202.4043247-4-houtao@huaweicloud.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>