net/sched: sch_dualpi2: Add missing module alias

When a qdisc is added by name, the kernel tries to autoload its module
via request_qdisc_module(), which calls:

request_module(NET_SCH_ALIAS_PREFIX "%s", name);

i.e. it asks modprobe to resolve the "net-sch-<kind>" alias (e.g.
"net-sch-dualpi2") rather than the module's file name. Since dualpi2
was shipped without this alias, the autoload fails:

tc qdisc add dev lo root handle 1: dualpi2
Error: Specified qdisc kind is unknown.

Fix this by adding the missing alias so the qdisc is autoloaded on demand
like the others.

Fixes: 320d031ad6e4 ("sched: Struct definition and parsing of dualpi2 qdisc")
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Reviewed-by: Pedro Tammela <pctammela@mojatatu.com>
Link: https://patch.msgid.link/20260611205849.3287640-1-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>