[CSL-742] Fix limit for GtMsgContents
[CSL-742] Fix limit for GtMsgContents

Since it's used inside `InvOrData` which adds 1-byte prefix,
chosen limit should depend on second byte.

input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/cardano-sl