Missing Macros in packet.h

Problem:
mac/mac-sensor.cc: In member function `void MacSensor::send(Packet*, Handler*)
':
mac/mac-sensor.cc:106: error: `HDR_MACSensor' undeclared (first use this
function)
mac/mac-sensor.cc:106: error: (Each undeclared identifier is reported only once
for each function it appears in.)
make: *** [mac/mac-sensor.o] Error 1

Fix:
Put the following missing macros in packet.h next to the other HDR macros:

#ifdef MIT_uAMPS
#define HDR_RCA(p) ((struct hdr_rca*)(p)->access(hdr_rca::offset_))
#define HDR_MACSensor(p) ((struct hdr_macSensor*)(p)->access(hdr_mac::offset_))
#endif