ifconfig: fix reporting optics on most 100g interfaces

This fixes a bug where optics on 100G and faster NICs
were not properly reported.

The problem is that we pull the string from the correct
table in ifconfig_sfp_physical_spec only when sfp_eth_1040g
contains the SFP_ETH_1040G_EXTENDED bit. However, we were
never saving that bit when it was encountered. This change
records that bit into sfp_eth_1040g, allowing us to later
select the appropriate ID string.

This should cause most 100G interfaces to stop being identified
as "unknown" in the "plugged" output of ifconfig -v, and to
start being identified as what they really are.

Example output from a Chelsio T6 with SR4 optics in one port
and DR1 optics in another:

Before:
plugged: QSFP28 Unknown (MPO 1x12 Parallel Optic)
plugged: QSFP28 Unknown (LC)

After:
plugged: QSFP28 100GBASE-SR4 or 25GBASE-SR (MPO 1x12 Parallel Optic)
plugged: QSFP28 100GBASE-DR (LC)

Reviewed by: kbowling, np
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D49127
MFC after: 7 days