net/virtio: fix untrusted scalar value

net/virtio: fix untrusted scalar value

The unscrutinized value may be incorrectly assumed to be within a certain
range by later operations.

In vhost_user_read: An unscrutinized value from an untrusted source used
in a trusted context - the value of sz_payload may be harmfull and we need
limit them to the max value of payload.

Coverity issue: 139601
Fixes: 6a84c37e3975 ("net/virtio-user: add vhost-user adapter layer")
Cc: stable@dpdk.org
Signed-off-by: Daniel Mrzyglod <danielx.t.mrzyglod@intel.com>
Acked-by: Jianfeng Tan <jianfeng.tan@intel.com>
Acked-by: Yuanhan Liu <yliu@fridaylinux.org>