qede: refactor XDP Tx processing

Current XDP Tx logic is suboptimal and can't be reused for XDP_REDIRECT
path.
Make qede_xdp_{tx_int,xmit}() more universal and effective in general to
allow future expanding.

Misc: use unlikely() hints where appropriate and replace "fallthrough"
comments with pseudo-keywords.

Signed-off-by: Alexander Lobakin <alobakin@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: Michal Kalderon <michal.kalderon@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>