net: stmmac: Drop redundant skb_mark_for_recycle() for SKB frags

After commit df542f66 ("net: stmmac: Switch to zero-copy in
non-XDP RX path"), SKBs are always marked for recycle, it is redundant
to mark SKBs more than once when new frags are appended.

Signed-off-by: Furong Xu <0x1207@gmail.com>
Link: https://patch.msgid.link/20250117062805.192393-1-0x1207@gmail.com


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