Fix fraggap accounting in the paged-allocation paths of IPv4 and IPv6.

The IPv6 patch is the v4 update of the previously posted patch. The IPv4
patch handles the same code pattern (by Ido).

v3->v4
- Remove the MSG_SPLICE_PAGES exception from the IPv6 negative copy check.
- Clarify where the fraggap bytes are copied in the commit messages.
- Add Reviewed-by tags.

v2->v3
- Add the IPv4 counterpart.
- Mention that the IPv6 corruption became triggerable after ce650a166335.
- Remove the stale comments about copy becoming -fraggap when pagedlen > 0.
- Add missing Cc entries.

v1->v2:
- Fix mail format.

v3: https://lore.kernel.org/netdev/aiq3f7UZGFp0F3MV@DESKTOP-19IMU7U.localdomain/ (local)
v2: https://lore.kernel.org/netdev/aigx83czv+UJZA0d@DESKTOP-19IMU7U.localdomain/ (local)
v1: https://lore.kernel.org/netdev/aibiIYMAwUErTw5U@DESKTOP-19IMU7U.localdomain/ (local)

Wongi Lee (2):
  ipv4: account for fraggap on the paged allocation path
  ipv6: account for fraggap on the paged allocation path

 net/ipv4/ip_output.c  | 7 ++-----
 net/ipv6/ip6_output.c | 9 +++------
 2 files changed, 5 insertions(+), 11 deletions(-)

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2.34.1