Some code quality patches for sdk 17.0.2

[mgux]

Hi,

please find attached some patches to improve the code quality of the SDK

1. Make ble_db_discovery_evt_t a const ptr

0001-Add-missing-const-for-ble_db_discovery_evt_t.patch

2. make p_string in ble_nus_c_string_send a const ptr

0001-Use-const-char-for-ble_nus_c_string_send.patch

3. Fix BLE_NUS_DEF macro for C++0001-Fix-BLE_NUS_DEF-macro-for-C.patch

4. Fix some warnings because of signed / unsigned

0001-Fix-warnings.patch

0001-Use-bitwise-operators-only-on-unsigned-operands.patch

5. Invalidate characteristic and cccd handles too

0001-Invalidate-characteristic-and-cccd-handles.patch

Best regards

[Simonr]

Thank you for your suggestions, I've reported this internally for review, but I can't guarantee when these patches will find themselves into an official SDK release. 

Best regards,

Simon