/*
* SADB_X_SPDACQUIRE processing.
* Acquire policy and SA(s) for a *OUTBOUND* packet.
* send
* <base, policy(*)>
* to KMD, and expect to receive
* <base> with SADB_X_SPDACQUIRE if error occurred,
* or
* <base, policy>
* with SADB_X_SPDUPDATE from KMD by PF_KEY.
* policy(*) is without policy requests.
*
* 0 : succeed
* others: error number
*/