Currently, when calculating block's bloom, we loop through all the
receipt logs to calculate the hash value. However, normally, after going
through applyTransaction, the receipt's bloom is already calculated
based on the receipt log, so the block's bloom can be calculated by just
ORing these receipt's blooms.
```
goos: darwin
goarch: arm64
pkg: github.com/ethereum/go-ethereum/core/types
cpu: Apple M1 Pro
BenchmarkCreateBloom
BenchmarkCreateBloom/small
BenchmarkCreateBloom/small-10             810922              1481 ns/op             104 B/op          5 allocs/op
BenchmarkCreateBloom/large
BenchmarkCreateBloom/large-10               8173            143764 ns/op            9614 B/op        401 allocs/op
BenchmarkCreateBloom/small-mergebloom
BenchmarkCreateBloom/small-mergebloom-10                 5178918               232.0 ns/op             0 B/op          0 allocs/op
BenchmarkCreateBloom/large-mergebloom
BenchmarkCreateBloom/large-mergebloom-10                   54110             22207 ns/op               0 B/op          0 allocs/op
```

---------

Co-authored-by: Gary Rong <[email protected]>
Co-authored-by: Zsolt Felfoldi <[email protected]>

This fixes a regression introduced in #31153 where we didn't consider
mainnet to be in PoS, causing #31190.
The problem is, `params.MainnetChainConfig` does not have a defined
`MergeNetsplitBlock`, so it isn't considered to be in PoS in
`CalcDifficulty`.

This fixes an issue where a nat.Interface unmarshaled from the TOML
config file could not be re-marshaled to TOML correctly.

Fixes #31183

We somehow forgot to add this in #30302, so discv5 and DNS have actually
been disabled since then.

Fixes #31168