Function syndrome_check 

pub fn syndrome_check(code: &LdpcCode, codeword: &[u8]) -> bool

Checks if hard decisions satisfy all parity checks.

codeword is n bits packed in n/8 bytes. Returns true if valid.

Internally recovers the punctured bits (last H-matrix column) from row 2 of the parity check matrix (which has an identity block for the punctured column), then verifies rows 0 and 1.