net: llc: Correct function name llc_sap_action_unitdata_ind() in header

Fix the following make W=1 kernel build warning:

  net/llc/llc_s_ac.c:38: warning: expecting prototype for llc_sap_action_unit_data_ind(). Prototype was for llc_sap_action_unitdata_ind() instead

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>