core, params: define london block at 12965000

[holiman]

This PR adds mainnet london fork block at 12965000.

[karalabe]

Also gonna need

@@ -203,11 +205,11 @@ func TestValidation(t *testing.T) {
                // Local is mainnet Petersburg, remote is Rinkeby Petersburg.
                {7987396, ID{Hash: checksumToBytes(0xafec6b27), Next: 0}, ErrLocalIncompatibleOrStale},
 
-               // Local is mainnet Berlin, far in the future. Remote announces Gopherium (non existing fork)
+               // Local is mainnet London, far in the future. Remote announces Gopherium (non existing fork)
                // at some future block 88888888, for itself, but past block for local. Local is incompatible.
                //
                // This case detects non-upgraded nodes with majority hash power (typical Ropsten mess).
-               {88888888, ID{Hash: checksumToBytes(0x0eb440f6), Next: 88888888}, ErrLocalIncompatibleOrStale},
+               {88888888, ID{Hash: checksumToBytes(0xb715077d), Next: 88888888}, ErrLocalIncompatibleOrStale},
 
                // Local is mainnet Byzantium. Remote is also in Byzantium, but announces Gopherium (non existing
                // fork) at block 7279999, before Petersburg. Local is incompatible.

[karalabe]

LGTM