if_bnxt: Implementation of Extended Port Hardware Stats Support for THOR Controller

The newly added port extended hardware statistics are now accessible to
users through the sysctl interface. Also, Few obsolete stats are removed
and few stats are renamed.

Reviewed by: imp
Approved by: imp
Differential revision: https://reviews.freebsd.org/D42957

(cherry picked from commit d36b36621a9c0f785ebea495c57e975b8a526b67)