RDMA/core: Rename rdma_copy_addr to rdma_copy_src_l2_addr

Now that rdma_copy_addr() only copies the source addresses and all callers
are interested in copying only source addresses, simplify it to drop the
destination address argument.

Given that it only copies source layer2 addresses, rename it to
rdma_copy_src_l2_addr for better code readability.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Daniel Jurgens <danielj@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>