CVE-2025-21787: team: better TEAM_OPTION_TYPE_STRING validation

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

team: better TEAMOPTIONTYPESTRING validation

syzbot reported following splat [1]

Make sure user-provided data contains one nul byte.

[1] BUG: KMSAN: uninit-value in stringnocheck lib/vsprintf.c:633 [inline] BUG: KMSAN: uninit-value in string+0x3ec/0x5f0 lib/vsprintf.c:714 stringnocheck lib/vsprintf.c:633 [inline] string+0x3ec/0x5f0 lib/vsprintf.c:714 vsnprintf+0xa5d/0x1960 lib/vsprintf.c:2843 requestmodule+0x252/0x9f0 kernel/module/kmod.c:149 teammodeget drivers/net/team/teamcore.c:480 [inline] teamchangemode drivers/net/team/teamcore.c:607 [inline] teammodeoptionset+0x437/0x970 drivers/net/team/teamcore.c:1401 teamoptionset drivers/net/team/teamcore.c:375 [inline] teamnloptionssetdoit+0x1339/0x1f90 drivers/net/team/teamcore.c:2662 genlfamilyrcvmsgdoit net/netlink/genetlink.c:1115 [inline] genlfamilyrcvmsg net/netlink/genetlink.c:1195 [inline] genlrcvmsg+0x1214/0x12c0 net/netlink/genetlink.c:1210 netlinkrcvskb+0x375/0x650 net/netlink/afnetlink.c:2543 genlrcv+0x40/0x60 net/netlink/genetlink.c:1219 netlinkunicastkernel net/netlink/afnetlink.c:1322 [inline] netlinkunicast+0xf52/0x1260 net/netlink/afnetlink.c:1348 netlinksendmsg+0x10da/0x11e0 net/netlink/afnetlink.c:1892 socksendmsgnosec net/socket.c:718 [inline] socksendmsg+0x30f/0x380 net/socket.c:733 syssendmsg+0x877/0xb60 net/socket.c:2573 syssendmsg+0x28d/0x3c0 net/socket.c:2627 syssendmsg net/socket.c:2659 [inline] dosyssendmsg net/socket.c:2664 [inline] sesyssendmsg net/socket.c:2662 [inline] x64syssendmsg+0x212/0x3c0 net/socket.c:2662 x64syscall+0x2ed6/0x3c30 arch/x86/include/generated/asm/syscalls64.h:47 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xcd/0x1e0 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x77/0x7f