[rilmodem] Fix stk mem leaks
[rilmodem] Fix ussd mem leaks

Signed-off-by: Tommi Kenakkala <tommi.kenakkala@oss.tieto.com>
[rilmodem] Fix supplementary service mem leak

Signed-off-by: Tommi Kenakkala <tommi.kenakkala@oss.tieto.com>
Merge pull request #247 from tkenakka/leak

Fix rilmodem memory leaks