[inetstack] Bad Type Casting

[ppenna]

Description

In protocols::tcp::established::ControlBlock::receive_data() and potentially everywhere, we are casting fixed sizes to usize to perform some checks.

We should do the other way around.

[ppenna]

@BrianZill is this fixed?

[iyzhang]

I see that many places we do this because the value might get truncated if cast down to a smaller size. Should we first check that it is safe to cast?