CVE-2025-39812: sctp: initialize more fields in sctp_v6_from_sk()

In the Linux kernel, the following vulnerability has been resolved:

sctp: initialize more fields in sctpv6fromsk()

syzbot found that sin6scopeid was not properly initialized, leading to undefined behavior.

Clear sin6scopeid and sin6flowinfo.

BUG: KMSAN: uninit-value in sctpv6cmpaddr+0x887/0x8c0 net/sctp/ipv6.c:649 sctpv6cmpaddr+0x887/0x8c0 net/sctp/ipv6.c:649 sctpinet6cmpaddr+0x4f2/0x510 net/sctp/ipv6.c:983 sctpbindaddrconflict+0x22a/0x3b0 net/sctp/bindaddr.c:390 sctpgetportlocal+0x21eb/0x2440 net/sctp/socket.c:8452 sctpgetport net/sctp/socket.c:8523 [inline] sctplistenstart net/sctp/socket.c:8567 [inline] sctpinetlisten+0x710/0xfd0 net/sctp/socket.c:8636 syslistensocket net/socket.c:1912 [inline] syslisten net/socket.c:1927 [inline] dosyslisten net/socket.c:1932 [inline] sesyslisten net/socket.c:1930 [inline] x64syslisten+0x343/0x4c0 net/socket.c:1930 x64syscall+0x271d/0x3e20 arch/x86/include/generated/asm/syscalls64.h:51 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xd9/0x210 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f

Local variable addr.i.i created at: sctpgetport net/sctp/socket.c:8515 [inline] sctplistenstart net/sctp/socket.c:8567 [inline] sctpinetlisten+0x650/0xfd0 net/sctp/socket.c:8636 syslistensocket net/socket.c:1912 [inline] syslisten net/socket.c:1927 [inline] dosyslisten net/socket.c:1932 [inline] sesyslisten net/socket.c:1930 [inline] x64syslisten+0x343/0x4c0 net/socket.c:1930