+/* dtls1_enc encrypts/decrypts the record in |s->wrec| / |s->rrec|, respectively.
+ *
+ * Returns:
+ * 0: (in non-constant time) if the record is publically invalid (i.e. too
+ * short etc).
+ * 1: if the record's padding is valid / the encryption was successful.
+ * -1: if the record's padding/AEAD-authenticator is invalid or, if sending,
+ * an internal error occurred. */