Fixed fragment data size in IPv6 defragmentation #6270

Job	Run time
Code health check	1m 16s
CodeQL analysis	2m 47s
Build doc	5m 35s
pyca/cryptography test	24s
Type hints check	27s
ubuntu-latest 3.7 non_root -K scanner	1m 51s
ubuntu-latest 3.8 non_root -K scanner	1m 47s
ubuntu-latest 3.9 non_root -K scanner	2m 5s
ubuntu-latest 3.10 non_root -K scanner	1m 45s
ubuntu-latest 3.11 non_root -K scanner	1m 43s
ubuntu-latest 3.12 non_root -K scanner	2m 20s
ubuntu-latest 3.12 root -K scanner	2m 26s
ubuntu-latest pypy3.9 root -K scanner	3m 3s
ubuntu-latest libpcap 3.12 root -K scanner	2m 9s
macos-12 3.12 both -K scanner	3m 27s
ubuntu-latest 3.12 root -k scanner	4m 2s
ubuntu-latest pypy3.9 root -k scanner	3m 8s
macos-12 3.12 both -k scanner	3m 40s
	43m 55s

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