Revert "bnxt_en: bring back rtnl_lock() in the bnxt_open() path"

Revert "bnxt_en: bring back rtnl_lock() in the bnxt_open() path"

This reverts commit 325eb217e41fa14f307c7cc702bd18d0bb38fe84.

udp_tunnel infra doesn't need RTNL, should be safe to get back
to only netdev instance lock.

Cc: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
Link: https://patch.msgid.link/20250616162117.287806-7-stfomichev@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>