[SysApps] Initialize UDPSocketObject's members in order.

Fixes a -Wreorder warning:

In file included from ../../../../home/abuild/rpmbuild/BUILD/crosswalk/src/xwalk/sysapps/raw_socket/udp_socket_object.cc:5:0:
../../../../home/abuild/rpmbuild/BUILD/crosswalk/src/xwalk/sysapps/raw_socket/udp_socket_object.h: In constructor 'xwalk::sysapps::UDPSocketObject::UDPSocketObject()':
../../../../home/abuild/rpmbuild/BUILD/crosswalk/src/xwalk/sysapps/raw_socket/udp_socket_object.h:54:33: warning: 'xwalk::sysapps::UDPSocketObject::resolver_' will be initialized after [-Wreorder]
   scoped_ptr<net::HostResolver> resolver_;
                                 ^
../../../../home/abuild/rpmbuild/BUILD/crosswalk/src/xwalk/sysapps/raw_socket/udp_socket_object.h:48:32: warning:   'scoped_refptr<net::IOBuffer> xwalk::sysapps::UDPSocketObject::read_buffer_' [-Wreorder]
   scoped_refptr<net::IOBuffer> read_buffer_;
                                ^
../../../../home/abuild/rpmbuild/BUILD/crosswalk/src/xwalk/sysapps/raw_socket/udp_socket_object.cc:25:1: warning:   when initialized here [-Wreorder]
 UDPSocketObject::UDPSocketObject()
 ^