CVE-2022-29189: Pion/DTLS contains buffer for inbound DTLS fragments with no limit

The vulnerability stems from uncontrolled buffering of inbound DTLS fragments. The commit a6397ff added critical size checks to fragmentBuffer.push() and introduced fragmentBuffer.size(), indicating this was the vulnerable area. The CWE-120 classification matches unbounded buffer growth in network input handling. The patch specifically modifies the push method to enforce a 2MB limit, confirming this function's role in the vulnerability. The associated test in fragment_buffer_test.go validates the overflow protection, further confirming the function's central role.