uint8_t macaddr[5][6] =
{
{0x01, 0x01, 0x01, 0x01, 0x01, 0x01}//1
,{0x02, 0x02, 0x02, 0x02, 0x02, 0x02}//2
,{0xaa, 0xaa, 0xaa, 0xaa, 0xaa, 0xaa}//3
,{0xbb, 0xbb, 0xbb, 0xbb, 0xbb, 0xbb}//4
,{0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc}//5
};

struct alarminfo
{
     uint8_t bssid[6];
     //
     //.....
};

alarminfo alarm_preset[5];

struct alarminfo *dst = alarm_preset;
for (uint8_t (*src)[6] = macaddr, (*src_end)[6] = src + 5; src != src_end;
       ++src, ++dst)
  memcpy(dst->bssid, src, sizeof *src);

for (unsigned i = 0; i < 5; ++i)
  memcpy(alarm_preset[i].bssid, macaddr[i], sizeof macaddr[i]);

struct alarminfo {
     uint8_t bssid[6];
     //...
};

struct alarminfo alarm_preset[5] = {
      {{0x01, 0x01, 0x01, 0x01, 0x01, 0x01}},  //1
      {{0x02, 0x02, 0x02, 0x02, 0x02, 0x02}},  //2
      {{0xaa, 0xaa, 0xaa, 0xaa, 0xaa, 0xaa}},  //3
      {{0xbb, 0xbb, 0xbb, 0xbb, 0xbb, 0xbb}},  //4
      {{0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc}}   //5
    }