Changed handling of IP addr in payload tests

Other general improvements, like noting that eventually eyeball with
the NOMATE mode will inform sensor that it has been rejected
Changed SG_TEST_COMM enum from READ to WRITE

Before it was right from a testing perspective: with
SG_TEST_COMM_READ_SPI, we are reading from the named spi pipe.
Now, it is right from an implementation perspective: with
SG_TEST_COMM_WRITE_SPI, we are writing to the serial line (and for
testing, we'll be reading that fifo). They both mean the same thing,
the WRITE just makes more sense