hostapd: fix ucode memory leak with strings

hostapd: fix ucode memory leak with strings

This fixes a common reference counting bug typically along the lines of:
```
uc_value_push(ucv_get(ucv_string_new(...)));
```
This would leave our new string with a reference count of 2, one from
the construction of the string, the other from `ucv_get`. This would
prevent the strings from being correctly cleaned up when it goes out
of scope.

Signed-off-by: Matthew Cather <mattbob4@gmail.com>