Added check for data size for TX write is less than 1MB.
Added check for data size for TX write is less than 1MB.

jblomer/ramcloud,utah-scs/RAMCloud,anirajk/RAMCloud,SMatsushi/RAMCloud,anirajk/RAMCloud,SMatsushi/RAMCloud,anirajk/RAMCloud,jblomer/ramcloud,SMatsushi/RAMCloud,utah-scs/RAMCloud,anirajk/RAMCloud,anirajk/RAMCloud,SMatsushi/RAMCloud,anirajk/RAMCloud,SMatsushi/RAMCloud,jblomer/ramcloud,jblomer/ramcloud,utah-scs/RAMCloud,utah-scs/RAMCloud,jblomer/ramcloud,SMatsushi/RAMCloud,utah-scs/RAMCloud,jblomer/ramcloud,utah-scs/RAMCloud