bng_en: Add TX support

bng_en: Add TX support

Add functions to support xmit along with TSO/GSO.
Also, add functions to handle TX completion events in the NAPI context.
This commit introduces the fundamental transmit data path

Signed-off-by: Bhargava Marreddy <bhargava.marreddy@broadcom.com>
Reviewed-by: Vikas Gupta <vikas.gupta@broadcom.com>
Reviewed-by: Rajashekar Hudumula <rajashekar.hudumula@broadcom.com>
Reviewed-by: Ajit Kumar Khaparde <ajit.khaparde@broadcom.com>
Reviewed-by: Rahul Gupta <rahul-rg.gupta@broadcom.com>
Link: https://patch.msgid.link/20260128185623.26559-5-bhargava.marreddy@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>