Make use of IP_VLAN_PCP setsockopt in ping and ping6.

[rscheff]

Summary

In order to validate the proper marking and use of a different
ethernet priority class, add the new session-specific PCP
feature to the ping/ping6 utilities.

This demonstrates the use of that new protocol option.

Depends upon D26409

Test Plan

Capture a ping icmp packet sent with the '-C pcp' option
via a real ethernet network interface. A 802.1Q tag header
with vlan id=0, and pcp=x should show up when decoding the
packet.

Furthermore, the verbose dump of the ICMP Echo Response
may include the 802.1p tag, if the receiving NIC delivered this up the
stack.

[rscheff]

tcpdump -i vmx0 -vvv -nn -e -XX icmp or \(vlan and icmp \) &
 
ping -C 5 -c 1 192.168.233.1


00:0c:29:f7:80:12 > e4:f4:c6:18:04:ed, ethertype 802.1Q (0x8100), length 102: vlan 0, p 5, ethertype IPv4, (tos 0x0, ttl 64, id 5252, offset 0, flags [none], proto ICMP (1), length 84)
  192.168.233.110 > 192.168.233.1: ICMP echo request, id 28676, seq 0, length 64
      0x0000:  e4f4 c618 04ed 000c 29f7 8012 8100 a000  ........).......  <== 8100 vlan tag, a0 00 ... PCP5, Vlan ID 0
      0x0010:  0800 4500 0054 1484 0000 4001 1264 c0a8  ..E..T....@..d..
      0x0020:  e96e c0a8 e901 0800 c769 7004 0000 0000  .n.......ip.....
      0x0030:  0510 26e4 a99a 0809 0a0b 0c0d 0e0f 1011  ..&.............
      0x0040:  1213 1415 1617 1819 1a1b 1c1d 1e1f 2021  ...............!
      0x0050:  2223 2425 2627 2829 2a2b 2c2d 2e2f 3031  "#$%&'()*+,-./01
      0x0060:  3233 3435 3637                           234567

[bcr]

Two minor corrections...

sbin/ping/ping.8

118

s/Add a/Add an/

(same for the other man page)

119

How about

s/use/uses/

for both cases in this sentence?

(same for the other man page)

[rscheff]

• improve man page grammar

[bcr]

OK for the man page part of the patch.

[mav]

Looks good to me.