Fail fast if the handshake type is unknown

In the SSLSocketInputRecord.decodeInputRecord() implementation:
    // skip the first byte: handshake type
    byte handshakeType = handshakeFrag.get();

The handshake type was not checked until the handshake message get fully parsed. It's nice to check that the handshake type is known here and fail fast.

Similar to SSLEngineInputRecord.decodeInputRecord() and DTLSInputRecord.parseHandshakeMessage().