MFC r270064,r270068,r270069,r270115,r270129,r270287,r270822,r271014,

MFC r270064,r270068,r270069,r270115,r270129,r270287,r270822,r271014,
  r271524,r273541,r282967,r283009,r283364.

Add support for reading i2c SFP/SFP+ data from NIC driver and
presenting most interesting fields via ifconfig -v.
This version supports Intel ixgbe driver only.

Tested on:      Cisco,Intel,Mellanox,ModuleTech,Molex transceivers

* Add new net/sff8436.h containing constants used to access
  QSFP+ data via i2c inteface. These constants has been taken
  from SFF-8436 "QSFP+ 10 Gbs 4X PLUGGABLE TRANSCEIVER" standard
  rev 4.8.
* Add support for printing QSFP+ information from 40G NICs
  such as Chelsio T5.

Example:
cxl1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=ec07bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,.....>
        ether 00:07:43:28:ad:08
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        media: Ethernet 40Gbase-LR4 <full-duplex>
        status: active
        plugged: QSFP+ 40GBASE-LR4 (MPO Parallel Optic)
        vendor: OEM PN: OP-QSFP-40G-LR4 SN: 20140318001 DATE: 2014-03-18
        module temperature: 64.06 C voltage: 3.26 Volts
        lane 1: RX: 0.47 mW (-3.21 dBm) TX: 2.78 mW (4.46 dBm)
        lane 2: RX: 0.20 mW (-6.94 dBm) TX: 2.80 mW (4.47 dBm)
        lane 3: RX: 0.18 mW (-7.38 dBm) TX: 2.79 mW (4.47 dBm)
        lane 4: RX: 0.90 mW (-0.45 dBm) TX: 2.80 mW (4.48 dBm)

Tested on:      Chelsio T5
Tested on:      Mellanox/Huawei passive/active cables/transceivers.

Sponsored by:   Yandex LLC

git-svn-id: svn://svn.freebsd.org/base/stable/10@286810 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f