net: splice: Drop unused @pipe

Since commit 41c73a0d ("net: speedup skb_splice_bits()"),
__splice_segment() and spd_fill_page() do not use the @pipe argument. Drop
it.

While adapting the callers, move one line to enforce reverse xmas tree
order.

No functional change intended.

Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://patch.msgid.link/20250702-splice-drop-unused-v3-1-55f68b60d2b7@rbox.co


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