RDMA/siw: use skb_crc32c() instead of __skb_checksum()

RDMA/siw: use skb_crc32c() instead of __skb_checksum()

Instead of calling __skb_checksum() with a skb_checksum_ops struct that
does CRC32C, just call the new function skb_crc32c().  This is faster
and simpler.

Acked-by: Leon Romanovsky <leon@kernel.org>
Reviewed-by: Bernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://patch.msgid.link/20250519175012.36581-5-ebiggers@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>