net: llc: make empty have static storage duration

net: llc: make empty have static storage duration

Make @empty have static storage duration (like net/sysctl_net.c does)
to avoid storing a bad pointer, and keep consistent with
__register_sysctl_table @table 'should not be free'd after registration'.

Note that this is _not_ a bug, since size is 0 the pointer will
never get deferenced.

Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260616064053.690154-1-guanwentao@uniontech.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>