IB/cm: Do not hold reference on cm_id unless needed

Typically, when the CM sends a MAD it bumps a reference count
on the associated cm_id.  There are some exceptions, such
as when the MAD is a direct response to a receive MAD.  For
example, the CM may generate an MRA in response to a duplicate
REQ.  But, in general, if a MAD may be sent as a result of
the user invoking an API call (e.g. ib_send_cm_rep(),
ib_send_cm_rtu(), etc.), a reference is taken on the cm_id.

This reference is necessary if the MAD requires a response.
The reference allows routing a response MAD back to the
cm_id, or, if no response is received, allows updating the
cm_id state to reflect the failure.

For MADs which do not generate a response from the
target, however, there's no need to hold a reference on the cm_id.
Such MADs will not be retried by the MAD layer and their
completions do not change the state of the cm_id.

There are 2 internal calls used to allocate MADs which take
a reference on the cm_id: cm_alloc_msg() and cm_alloc_priv_msg().
The latter calls the former.  It turns out that all other places
where cm_alloc_msg() is called are for MADs that do not generate
a response from the target: sending an RTU, DREP, REJ, MRA, or
SIDR REP.  In all of these cases, there's no need to hold a
reference on the cm_id.

The benefit of dropping unneeded references is that it allows
destruction of the cm_id to proceed immediately.  Currently,
the cm_destroy_id() call blocks as long as there's a reference
held on the cm_id.  Worse, is that cm_destroy_id() will send
MADs, which it then needs to complete.  Sending the MADs is
beneficial, as they notify the peer that a connection is
being destroyed.  However, since the MADs hold a reference
on the cm_id, they block destruction and cannot be retried.

Move cm_id referencing from cm_alloc_msg() to cm_alloc_priv_msg().
The latter should hold a reference on the cm_id in all cases but
one, which will be handled in a separate patch.  cm_alloc_priv_msg()
is used when sending a REQ, REP, DREQ, and SIDR REQ, all of which
require a response.

Also, merge common code into cm_alloc_priv_msg() and combine the
freeing of all messages which do not need a response.

Signed-off-by: Sean Hefty <shefty@nvidia.com>
Signed-off-by: Or Har-Toov <ohartoov@nvidia.com>
Signed-off-by: Vlad Dumitrescu <vdumitrescu@nvidia.com>
Link: https://patch.msgid.link/1f0f96acace72790ecf89087fc765dead960189e.1731495873.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>

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