if_bnxt: Set 1G/10G baseT force speed as auto speeds

The firmware lacks support for manually setting 1G and 10G baseT speeds.
However, the driver can enable auto speed masks to achieve automatic configuration
at these speeds.

Reviewed by: imp
Approved by: imp
Differential revision: https://reviews.freebsd.org/D42960

(cherry picked from commit 770e7ba3ebe87ba7ffc872c87de72707757b4e25)