Revert 4a08e08..6915fb5

This rolls back to commit 4a08e08e4d6c1e7f4343bc5332324eb1888d2564.
Revert "Merge pull request #24 from s3lsensor/yzliao_v0.2_mac_hdr"

This reverts commit 4a08e08e4d6c1e7f4343bc5332324eb1888d2564, reversing
changes made to 2c849364fe5fb94d167ae6668ce28a955375b7f7.

Conflicts:
	core/net/appconn/app_conn.c
	core/net/appconn/app_conn.h
	hello_world/nullApp.c
	hello_world/project-conf.h
	s3l_rdc/tdmardc.c