NetworkPkg: Add dns support for target URL configuration in ISCSI.

NetworkPkg: Add dns support for target URL configuration in ISCSI.

v2:
*1. Add IScsiDnsIsConfigured function in IScsiSupported to check
attempt using DNS protocol or not.2. Fix wrongs typos in IScsiDns.c
and .uni file.3. define a macro for the length of target URL.4.
update the Copyright to 2017.

Add DNS support for target URL directly configuration in UI.

Besides, When we enable the option (Get target info via DHCP) ,
the dhcp server will return target info include the  rootpath,
like the format
"iscsi:"<servername>":"<protocol>":"<port>":"<LUN>":"<targetname>
According to the RFC 4173,the server name region is expressed as
IPv4(192.168.10.20 )or IPv6 ([2000:bbbb::3]) or domain name,
but currently we only support the IP address format.
To enable this feature, we can support both.

Another enhancement is that we can deal with the data received from
the iSCSI login response with an target redirection status,
in which contains the Target Address in the format
domainname[:port][,portal-group-tag] required by RFC 3720.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Wu Jiaxin <jiaxin.wu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Zhang Lubo <lubo.zhang@intel.com>
Reviewed-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>