Policy contract's SetMaxTransactionsPerBlock() doesn't check for Block.MaxTransactionsPerBlock

[roman-khimov]

Describe the bug
Some policy values while being configurable are still limited by other hardcoded constraints, like SetMaxBlockSize() has to check the value passed against Network.P2P.Message.PayloadMaxSize, because it's not very useful to have blocks that couldn't be distributed via P2P.

SetMaxTransactionsPerBlock() at the moment allows any uint value to be set, but there are P2P limitations of MaxContentsPerBlock and MaxTransactionsPerBlock imposed by the Block class and setting policy value to some higher number would just create undeserializable block if anyone is to attempt to put this many transactions into it.

Expected behavior
SetMaxTransactionsPerBlock() should check the value passed against Block.MaxTransactionsPerBlock.

(Optional) Additional context
While we're here I'd also propose increasing Block.MaxTransactionsPerBlock two-fold. Given some typical 250-byte transactions a block with a length of Network.P2P.Message.PayloadMaxSize has enough space for just a little more than 128K of them.

Although even when the number of transactions per block is only limited by the payload size, some test results may look like this:

Still, 64K is not allowing to use all of PayloadMaxSize capacity.