e1000: Improve igb(4) SFP support

• Adds support for SFPs that are not correctly coded as an SFP transceiver. i.e. Coherent-Finisar FCLF8522P2BTL.
• Configures multi-rate SFPs i.e. Coherent-Finisar FCLF8522P2BTL as SGMII so they can do 10/100/1000 auto-negotiation.
• Adds support for 100BaseLX SGMII transceivers.
• Some code cleanup and additional debugging.

Reviewed by: emaste, markj, Franco Fichtner <franco@opnsense.org>
Tested by: Natalino Picone <natalino.picone@nozominetworks.com>
Sponsored by: Nozomi Networks
Sponsored by: BBOX.io
Differential Revision: https://reviews.freebsd.org/D47337

(cherry picked from commit 15853a5fc9548d9805a2ef22f24e2eb580198341)