Revert "vmci: Prevent the dispatching of uninitialized payloads"

[ Upstream commit 8f5d9bed6122b8d96508436e5ad2498bb797eb6b ]

This reverts commit bfb4cf9fb97e4063f0aa62e9e398025fb6625031.

While the code "looks" correct, the compiler has no way to know that
doing "fun" pointer math like this really isn't a write off the end of
the structure as there is no hint anywhere that the structure has data
at the end of it.

This causes the following build warning:

In function 'fortify_memset_chk',
    inlined from 'ctx_fire_notification.isra' at drivers/misc/vmw_vmci/vmci_context.c:254:3:
include/linux/fortify-string.h:480:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
  480 |                         __write_overflow_field(p_size_field, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

So revert it for now and it can come back in the future in a "sane" way
that either correctly makes the structure know that there is trailing
data, OR just the payload structure is properly referenced and zeroed
out.

Fixes: bfb4cf9fb97e ("vmci: Prevent the dispatching of uninitialized payloads")
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Lizhi Xu <lizhi.xu@windriver.com>
Link: https://lore.kernel.org/r/20250703171021.0aee1482@canb.auug.org.au


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>