[dhcpv6] Include vendor class identifier option in DHCPv6 requests

RFC3315 defines DHCPv6 option 16 (vendor class identifier) but does
not define any direct relationship with the roughly equivalent DHCPv4
option 60.

The PXE specification predates IPv6, and the UEFI specification is
expectedly vague on the subject.  Examination of the reference EDK2
codebase suggests that the DHCPv6 vendor class identifier will be
formatted in accordance with RFC3315, using a single vendor-class-data
item in which the opaque-data field is the string as would appear in
DHCPv4 option 60.

RFC3315 requires the vendor class identifier to specify an IANA
enterprise number, as a way of disambiguating the vendor-class-data
namespace.  The EDK2 code uses the value 343, described as:

    // TODO: IANA TBD: temporarily using Intel's

Since this "TODO" has been present since at least 2010, it is probably
safe to assume that it has now become a de facto standard.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/dhcpv6.h

 /** DHCPv6 user class option */
 #define DHCPV6_USER_CLASS 15
 
+/** DHCPv6 vendor class option */
+#define DHCPV6_VENDOR_CLASS 16
+
+/** DHCPv6 PXE vendor class
+ *
+ * The DHCPv6 vendor class includes a field for an IANA enterprise
+ * number.  The EDK2 codebase uses the value 343, with the comment:
+ *
+ *     TODO: IANA TBD: temporarily using Intel's
+ *
+ * Since this "temporarily" has applied since at least 2010, we assume
+ * that it has become a de facto standard.
+ */
+#define DHCPV6_VENDOR_CLASS_PXE 343
+
 /** DHCPv6 DNS recursive name server option */
 #define DHCPV6_DNS_SERVERS 23
 
  */
 #define DHCPV6_LOG_SERVERS 0xffffffffUL
 
+/** Construct a DHCPv6 byte value */
+#define DHCPV6_BYTE_VALUE( value ) ( (value) & 0xff )
+
+/** Construct a DHCPv6 word value */
+#define DHCPV6_WORD_VALUE( value ) \
+	DHCPV6_BYTE_VALUE ( (value) >> 8 ), DHCPV6_BYTE_VALUE ( (value) >> 0 )
+
+/** Construct a DHCPv6 dword value */
+#define DHCPV6_DWORD_VALUE( value ) \
+	DHCPV6_WORD_VALUE ( (value) >> 16 ), DHCPV6_WORD_VALUE ( (value) >> 0 )
+
 /** Construct a DHCPv6 option code */
-#define DHCPV6_CODE( code ) \
-	( ( (code) >> 8 ) & 0xff ), ( ( (code) >> 0 ) & 0xff )
+#define DHCPV6_CODE( code ) DHCPV6_WORD_VALUE ( code )
 
 /** Construct a DHCPv6 option length */
-#define DHCPV6_LEN( len ) \
-	( ( (len) >> 8 ) & 0xff ), ( ( (len) >> 0 ) & 0xff )
+#define DHCPV6_LEN( len ) DHCPV6_WORD_VALUE ( len )
 
 /** Construct a DHCPv6 option from a list of bytes */
 #define DHCPV6_OPTION( ... ) \
 #define DHCPV6_STRING( ... ) DHCPV6_OPTION ( __VA_ARGS__ )
 
 /** Construct a byte-valued DHCPv6 option */
-#define DHCPV6_BYTE( value ) DHCPV6_OPTION ( value )
+#define DHCPV6_BYTE( value ) DHCPV6_OPTION ( DHCPV6_BYTE_VALUE ( value ) )
 
 /** Construct a word-valued DHCPv6 option */
-#define DHCPV6_WORD( value ) DHCPV6_OPTION ( ( ( (value) >> 8 ) & 0xff ), \
-					     ( ( (value) >> 0 ) & 0xff ) )
+#define DHCPV6_WORD( value ) DHCPV6_OPTION ( DHCPV6_WORD_VALUE ( value ) )
+
 /** Construct a dword-valued DHCPv6 option */
-#define DHCPV6_DWORD( value ) DHCPV6_OPTION ( ( ( (value) >> 24 ) & 0xff ), \
-					      ( ( (value) >> 16 ) & 0xff ), \
-					      ( ( (value) >>  8 ) & 0xff ), \
-					      ( ( (value) >>  0 ) & 0xff ) )
+#define DHCPV6_DWORD( value ) DHCPV6_OPTION ( DHCPV6_DWORD_VALUE ( value ) )
 
 /**
  * Any DHCPv6 option

src/net/udp/dhcpv6.c

 			DHCPV6_CODE ( DHCPV6_DOMAIN_LIST ),
 			DHCPV6_CODE ( DHCPV6_BOOTFILE_URL ),
 			DHCPV6_CODE ( DHCPV6_BOOTFILE_PARAM ) ),
+	DHCPV6_CODE ( DHCPV6_VENDOR_CLASS ),
+	DHCPV6_OPTION ( DHCPV6_DWORD_VALUE ( DHCPV6_VENDOR_CLASS_PXE ),
+			DHCPV6_STRING ( DHCP_ARCH_VENDOR_CLASS_ID ) ),
 	DHCPV6_CODE ( DHCPV6_CLIENT_ARCHITECTURE ),
 	DHCPV6_WORD ( DHCP_ARCH_CLIENT_ARCHITECTURE ),
 	DHCPV6_CODE ( DHCPV6_CLIENT_NDI ),