NetworkPkg: Fix incorrect unicode string of the AKM/Cipher Suite

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3813



The size of buffer should be 3 CHAR16 for Null-terminated Unicode
string.
The first char is the AKM/Cipher Suite number, the second char is ' ',
the third char is '\0'.

Cc: Maciej Rabeda <maciej.rabeda@linux.intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Wu Jiaxin <jiaxin.wu@intel.com>
Signed-off-by: Heng Luo <heng.luo@intel.com>
Reviewed-by: Maciej Rabeda <maciej.rabeda@linux.intel.com>