net/rds: Restrict use of RDS/IB to the initial network namespace

net/rds: Restrict use of RDS/IB to the initial network namespace

Prevent using RDS/IB in network namespaces other than the initial one.
The existing RDS/IB code will not work properly in non-initial network
namespaces.

Fixes: d5a8ac28a7ff ("RDS-TCP: Make RDS-TCP work correctly when it is set up in a netns other than init_net")
Reported-by: syzbot+da8e060735ae02c8f3d1@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=da8e060735ae02c8f3d1
Signed-off-by: Greg Jumper <greg.jumper@oracle.com>
Signed-off-by: Allison Henderson <achender@kernel.org>
Link: https://patch.msgid.link/20260408080420.540032-3-achender@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>