Remove duplicate varbles

Several variables within structures contain the same information in
different forms.

The aircraft structure contains addr and hexaddr. Hexaddr is a printable
string version of addr. However, hexaddr is only ever used in printf
statments, so we can use printf(%06x) to print addr. This saves a printf
for every received command.

The modesMessage structure contains addr, and aa1,aa2,aa3 as separate
bytes. aa1,aa2 and aa3 are only ever used to construct addr, and to
print out. Therefore, we can use addr instead of them..