[qca-nss-clients] Issues fixed in OVPN manager

issues fixed:
- NULL check added for control msg received from application
- Initialization of statistics memory before accessing.
- Check for duplicate route add

Change-Id: I009b6a53659845dbf48e194d30bce7f39867c91d
Signed-off-by: Bhaskar Valaboju <bhaskarv@codeaurora.org>
3 files changed