Encoding:
    SILC_ASN1_ENUM(enum)
    SILC_ASN1_ENUM_T(opts, tag, &enum)

    Decoding:
    SILC_ASN1_ENUM(&enum)
    SILC_ASN1_ENUM_T(opts, tag, &enum);

    Macro used to encode or decode enumeration value.  The enumeration
    type is SilcMPInt.

    The `opts' is SilcAsn1Options.  The `tag' is a tag number.