queue_api: reduce risk of name collision over txq

Rename local variable in macros from txq to _txq.
When macro parameter get_desc is expended it is likely to have a txq
token that refers to a different txq variable at the caller's site.

Signed-off-by: Gur Stavi <gur.stavi@huawei.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/95b60d218f004308486d92ed17c8cc6f28bac09d.1747559621.git.gur.stavi@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>