Adding stdbool header include to netmaster example client to fix compile...

Here is a pull request to fix a compile error while working with gcc version 4.6.3 on the wandboard running kernel 3.13.0-armv7-x9.

The compiler picked up this error:

../example-clients/netmaster.c: In function ‘main’:
../example-clients/netmaster.c:104:86: error: ‘true’ undeclared (first use in this function)
../example-clients/netmaster.c:104:86: note: each undeclared identifier is reported only once for each function it appears in

Thanks.