net/sched: cls_api: Move call to tcf_exts_miss_cookie_base_destroy()

When CONFIG_NET_CLS_ACT is disabled:

  ../net/sched/cls_api.c:141:13: warning: 'tcf_exts_miss_cookie_base_destroy' defined but not used [-Wunused-function]
    141 | static void tcf_exts_miss_cookie_base_destroy(struct tcf_exts *exts)
        |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Due to the way the code is structured, it is possible for a definition
of tcf_exts_miss_cookie_base_destroy() to be present without actually
being used. Its single callsite is in an '#ifdef CONFIG_NET_CLS_ACT'
block but a definition will always be present in the file. The version
of tcf_exts_miss_cookie_base_destroy() that actually does something
depends on CONFIG_NET_TC_SKB_EXT, so the stub function is used in both
CONFIG_NET_CLS_ACT=n and CONFIG_NET_CLS_ACT=y + CONFIG_NET_TC_SKB_EXT=n
configurations.

Move the call to tcf_exts_miss_cookie_base_destroy() in
tcf_exts_destroy() out of the '#ifdef CONFIG_NET_CLS_ACT', so that it
always appears used to the compiler, while not changing any behavior
with any of the various configuration combinations.

Fixes: 80cd22c3

 ("net/sched: cls_api: Support hardware miss to tc action")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>