su: fix su_time() on 64-bit OS X
su: fix su_time() on 64-bit OS X

The field tv_sec in struct timeval is 64bits instead of 32bits as in
su_time_t, so you cannot cast su_time_t to struct timeval.

BelledonneCommunications/sofia-sip,BelledonneCommunications/sofia-sip,BelledonneCommunications/sofia-sip,unispeech/sofia-sip,unispeech/sofia-sip,BelledonneCommunications/sofia-sip,unispeech/sofia-sip,unispeech/sofia-sip