net: sched: wrap tc_skip_wrapper with CONFIG_RETPOLINE

This patch fixes the following sparse warning:

net/sched/sch_api.c:2305:1: sparse: warning: symbol 'tc_skip_wrapper' was not declared. Should it be static?

No functional change intended.

Signed-off-by: Min-Hua Chen <minhuadotchen@gmail.com>
Acked-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>