net: make napi_frag_unref reuse skb_page_unref

net: make napi_frag_unref reuse skb_page_unref

The implementations of these 2 functions are almost identical. Remove
the implementation of napi_frag_unref, and make it a call into
skb_page_unref so we don't duplicate the implementation.

Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20240408153000.2152844-2-almasrymina@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>