Add IP(V6)_VLAN_PCP to set 802.1 priority per-flow.

This adds a new IP_PROTO / IPV6_PROTO setsockopt (getsockopt)
option IP(V6)_VLAN_PCP, which can be set to -1 (interface
default), or explicitly to any priority between 0 and 7.

Note that for untagged traffic, explicitly adding a
priority will insert a special 801.1Q vlan header with
vlan ID = 0 to carry the priority setting

Reviewed by:	gallatin, rrs
MFC after:	2 weeks
Sponsored by:	NetApp, Inc.
Differential Revision:	https://reviews.freebsd.org/D26409

newlib/libc/sys/rtems/include/netinet/in.h

@@ -483,6 +483,10 @@ __END_DECLS
 /* The following option is private; do not use it from user applications. */
 #define	IP_MSFILTER			74   /* set/get filter list */
 
+/* The following option deals with the 802.1Q Ethernet Priority Code Point */
+#define	IP_VLAN_PCP		75   /* int; set/get PCP used for packet, */
+				     /*      -1 use interface default */
+
 /* Protocol Independent Multicast API [RFC3678] */
 #define	MCAST_JOIN_GROUP		80   /* join an any-source group */
 #define	MCAST_LEAVE_GROUP		81   /* leave all sources for group */

newlib/libc/sys/rtems/include/netinet6/in6.h

@@ -387,6 +387,10 @@ struct route_in6 {
 				    * set/get multicast source filter list.
 				    */
 
+/* The following option deals with the 802.1Q Ethernet Priority Code Point */
+#define	IPV6_VLAN_PCP		75  /* int; set/get PCP used for packet, */
+				    /*      -1 use interface default */
+
 /* to define items, should talk with KAME guys first, for *BSD compatibility */
 
 #define IPV6_RTHDR_LOOSE     0 /* this hop need not be a neighbor. XXX old spec */