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