NetworkPkg: Enlarge receive block size of HTTP boot driver.

HTTP boot driver uses block size of 1024 when receiving HTTP message body,
but typically the MTU of Ethernet is 1500 bytes so it makes 1 TCP segment data
split into 2 Http.Response call. This patch enlarges the block size to avoid
this issue.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18447 6f19259b-4bc3-4df7-8a09-765794883524