net: bnxt: use ethtool string helpers

Avoids having to use manual pointer manipulation.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Link: https://patch.msgid.link/20241029233229.9385-1-rosenp@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>