iscsi/tgt_node: Fix truncation warning on clear-linux-os-33460

Compiling warning :
spdk/lib/iscsi/tgt_node.c:550:42: warning: ‘%s’ directive output may be truncated
writing up to 2927 bytes into a region of size 1024 [-Wformat-truncation=]
  550 |  snprintf(port_name, sizeof(port_name), "%s,t,0x%4.4x",
      |                                          ^~
In file included from /usr/include/stdio.h:867,

gcc -v:
gcc-10.1.0-290-gc32074f6de

Signed-off-by: yidong0635 <dongx.yi@intel.com>
Change-Id: I56fd5adfc461254751b54fd8610949e72ecbd8f7
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/3216


Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Community-CI: Mellanox Build Bot
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>