tipc: check attribute length for bearer name

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

tipc: check attribute length for bearer name

syzbot reported uninit-value:

=====================================================

BUG: KMSAN: uninit-value in string_nocheck lib/vsprintf.c:644 [inline]

BUG: KMSAN: uninit-value in string+0x4f9/0x6f0 lib/vsprintf.c:725

string_nocheck lib/vsprintf.c:644 [inline]

string+0x4f9/0x6f0 lib/vsprintf.c:725

vsnprintf+0x2222/0x3650 lib/vsprintf.c:2806

vprintk_store+0x537/0x2150 kernel/printk/printk.c:2158

vprintk_emit+0x28b/0xab0 kernel/printk/printk.c:2256

vprintk_default+0x86/0xa0 kernel/printk/printk.c:2283

vprintk+0x15f/0x180 kernel/printk/printk_safe.c:50

_printk+0x18d/0x1cf kernel/printk/printk.c:2293

tipc_enable_bearer net/tipc/bearer.c:371 [inline]

__tipc_nl_bearer_enable+0x2022/0x22a0 net/tipc/bearer.c:1033

tipc_nl_bearer_enable+0x6c/0xb0 net/tipc/bearer.c:1042

genl_family_rcv_msg_doit net/netlink/genetlink.c:731 [inline]

- Do sanity check the attribute length for TIPC_NLA_BEARER_NAME.

- Do not use 'illegal name' in printing message.