Merge branch 'net-rds-convert-rds-to-getsockopt_iter'

Breno Leitao says:

====================
net: rds: convert rds to getsockopt_iter

This series continues the conversion of the remaining proto_ops getsockopt
callbacks to the new getsockopt_iter callback introduced in commit
67fab22a7adc ("net: add getsockopt_iter callback to proto_ops"), this time
for RDS.

RDS is a little more involved than the protocols converted so far, because
the RDS_INFO_* options snapshot kernel state directly into the destination
buffer: the info producers memcpy into the pages under a spinlock via
kmap_atomic() and so must not fault.

The conversion preserves that model — it obtains the same page array and
starting offset from opt->iter_out with iov_iter_extract_pages(),
preallocating the array so the iterator fills it in place, and leaves
the rds_info_iterator / rds_info_copy machinery and all producer
callbacks unchanged; kernel (ITER_KVEC) buffers remain unsupported on
the RDS_INFO path, as before.

I've vibe-coded a kselftest exercising both the simple options and the
RDS_INFO_* snapshot path, feel free to drop it in case this is not
useful.

Signed-off-by: Breno Leitao <leitao@debian.org>
====================

Link: https://patch.msgid.link/20260608-getsock_more-v3-0-706ecf2ea332@debian.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>