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When a system receives a REREG event from the SM, then the SM information
in the kernel is marked as invalid and a request is sent to the SM to
update the information. The SM information is invalid in that time period.

However, receiving a REREG also occurs simultaneously in user space
applications that are now trying to rejoin the multicast groups. Some of
those may be sendonly multicast groups which are then failing.

If the SM information is invalid then ib_sa_sendonly_fullmem_support()
returns false. That is wrong because it just means that we do not know yet
if the potentially new SM supports sendonly joins.

Sendonly join was introduced in 2015 and all the Subnet managers have
supported it ever since. So there is no point in checking if a subnet
manager supports it.

Should an old opensm get a request for a sendonly join then the request
will fail. The code that is removed here accomodated that situation and
fell back to a full join.

Fall...