What exacly is BITCOIN_SEED_NONCE in Bitcoin Source code?

I'm studing blockchain and I'm curently looking at how to DNS Seed Nodes work. I understand that crawler grabs nodes via magic messages but I can't figure out where one value came from Bitcoin source code and what is use of it.

#define BITCOIN_SEED_NONCE 0x0539a019ca550825ULL Program source: https://github.com/team-exor/generic-seeder/blob/f6c33d59b9a56a677364fbcdb9b2e30c51fc4a89/bitcoin.cpp#L9

Could you guys help me figure this out and point to correct place in Bitcoin source and let me know what is exacly use of that hex number?

It is used by generic-seeder in it's PushVersion function, which corresponds to the "version" message used in handshakes between new bitcoin peers.

From the bitcoin wiki:

nonce uint64_t: Node random nonce, randomly generated every time a version packet is sent. This nonce is used to detect connections to self.

The PeerManagerImpl::PushNodeVersion(CNode& pnode, int64_t nTime) routine is the equivalent routine in the Bitcoin source:

void PeerManagerImpl::PushNodeVersion(CNode& pnode, int64_t nTime)
{
<...>
    uint64_t nonce = pnode.GetLocalNonce();
<...>
    m_connman.PushMessage(&pnode, CNetMsgMaker(INIT_PROTO_VERSION).Make(NetMsgType::VERSION, PROTOCOL_VERSION, (uint64_t)nLocalNodeServices, nTime, addrYou, addrMe,
            nonce, strSubVersion, nNodeStartingHeight, tx_relay));
<...>
}