net: unify alloclen calculation for paged requests

Consolidate alloclen and pagedlen calculation for zerocopy and normal
paged requests. The current non-zerocopy paged version can a bit
overallocate and unnecessary copy a small chunk of data into the linear
part.

Cc: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/netdev/CA+FuTSf0+cJ9_N_xrHmCGX_KoVCWcE0YQBdtgEkzGvcLMSv7Qw@mail.gmail.com/Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b0e4edb7b91f171c7119891d3c61040b8c56596e.1661428921.git.asml.silence@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/ipv4/ip_output.c

@@ -1109,10 +1109,7 @@ static int __ip_append_data(struct sock *sk,
 				 (fraglen + alloc_extra < SKB_MAX_ALLOC ||
 				  !(rt->dst.dev->features & NETIF_F_SG)))
 				alloclen = fraglen;
-			else if (!zc) {
-				alloclen = min_t(int, fraglen, MAX_HEADER);
-				pagedlen = fraglen - alloclen;
-			} else {
+			else {
 				alloclen = fragheaderlen + transhdrlen;
 				pagedlen = datalen - transhdrlen;
 			}

net/ipv6/ip6_output.c

@@ -1648,10 +1648,7 @@ static int __ip6_append_data(struct sock *sk,
 				 (fraglen + alloc_extra < SKB_MAX_ALLOC ||
 				  !(rt->dst.dev->features & NETIF_F_SG)))
 				alloclen = fraglen;
-			else if (!zc) {
-				alloclen = min_t(int, fraglen, MAX_HEADER);
-				pagedlen = fraglen - alloclen;
-			} else {
+			else {
 				alloclen = fragheaderlen + transhdrlen;
 				pagedlen = datalen - transhdrlen;
 			}