RDMA/srp: Apply the __packed attribute to members instead of structures

Applying the __packed attribute to an entire data structure results in
suboptimal code on architectures that do not support unaligned accesses.
Hence apply the __packed attribute only to those data members that are
not naturally aligned.

Link: https://lore.kernel.org/r/20210524041211.9480-4-bvanassche@acm.org


Cc: Nicolas Morey-Chaisemartin <nmoreychaisemartin@suse.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>