igb: Remove static qualifiers

Remove static qualifiers on the following functions to be able to call
from XSK specific file that is added in the later patches:
- igb_xdp_tx_queue_mapping()
- igb_xdp_ring_update_tail()
- igb_clean_tx_ring()
- igb_clean_rx_ring()
- igb_xdp_xmit_back()
- igb_process_skb_fields()

While at it, inline igb_xdp_tx_queue_mapping() and
igb_xdp_ring_update_tail(). These functions are small enough and used in
XDP hot paths.

Signed-off-by: Sriram Yagnaraman <sriram.yagnaraman@est.tech>
[Kurt: Split patches, inline small XDP functions]
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Tested-by: George Kuruvinakunnel <george.kuruvinakunnel@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://patch.msgid.link/20250106221929.956999-2-anthony.l.nguyen@intel.com


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