bxe: Add warpcore 2500baseX support

[adam.jaremko_freebsd_gmail.com]

Summary

Support 2500Base-X on NetXtreme II BCM5710 adapters according to NVRAM configuration

Test Plan

The hardware and nvram configuration have been thoroughly documented by myself at https://www.dslreports.com/forum/r32230041-Internet-Bypassing-the-HH3K-up-to-2-5Gbps-using-a-BCM57810S-NIC

[luca.piccirillo_gmail.com]

sys/dev/bxe/bxe_elink.c

5050

I cannot understand this bitmask conditions. It looks to me that you are enforcing 1G capability to be enabled in cap_mask even for 2_5G. Why?

[adam.jaremko_freebsd_gmail.com]

sys/dev/bxe/bxe_elink.c

5050

SFP+ transceivers must support 1G, be it if they're 2.5G, 10G, etc. and it should be present in the capability mask when fiddling with ediag and was used as a catch guard against misconfiguration.

This also aligns with some previous code handling 2.5G and how the MII control register is set for 1G. But it's not strictly required to include 1G capability in the mask for this condition.