loadable_sample/wifiapp: fix wrong syntax of #elif and build warnings
loadable_sample/wifiapp: fix wrong syntax of #elif and build warnings

1. Wrong usage of #elif
  CONFIG is defined when it is assigned to y. Otherwise it is undefined.
  In this case, #elif CONFIG_XX is a wrong usage.
  It should be checked by "defined( )".

2. Build Warnings
  The is_testing and ch local variables are used only in CONFIG_EXAMPLES_LOADABLE_MANUAL_TEST.
  Let's cover them with that conditional to fix below.

make[2]: Entering directory '/root/tizenrt/loadable_apps/loadable_sample/wifiapp'
CC: wifiapp.c
wifiapp.c: In function 'main':
wifiapp.c:63:7: warning: unused variable 'is_testing' [-Wunused-variable]
  bool is_testing = true;
       ^~~~~~~~~~
wifiapp.c:62:6: warning: unused variable 'ch' [-Wunused-variable]
  int ch;
      ^~

Signed-off-by: sunghan-chang <c954e25285721d8faa8b1a5c1ae2ef5a35338d32@samsung.com>

sunghan-chang/TizenRT,an4967/TizenRT,Samsung/TizenRT,jsdosa/TizenRT,junmin-kim/TizenRT,sunghan-chang/TizenRT,Samsung/TizenRT,junmin-kim/TizenRT,jeongchanKim/TizenRT,an4967/TizenRT,jeongchanKim/TizenRT,pillip8282/TizenRT,pillip8282/TizenRT,sunghan-chang/TizenRT,jeongarmy/TizenRT,an4967/TizenRT,sunghan-chang/TizenRT,jeongchanKim/TizenRT,Samsung/TizenRT,jsdosa/TizenRT,pillip8282/TizenRT,sunghan-chang/TizenRT,jeongchanKim/TizenRT,jeongarmy/TizenRT,jsdosa/TizenRT,pillip8282/TizenRT,sunghan-chang/TizenRT,pillip8282/TizenRT,Samsung/TizenRT,sunghan-chang/TizenRT,junmin-kim/TizenRT,jeongarmy/TizenRT,jeongchanKim/TizenRT,jsdosa/TizenRT,an4967/TizenRT,Samsung/TizenRT,Samsung/TizenRT,jsdosa/TizenRT,jeongchanKim/TizenRT,junmin-kim/TizenRT,an4967/TizenRT,jsdosa/TizenRT,jeongarmy/TizenRT,jeongarmy/TizenRT,jeongarmy/TizenRT,an4967/TizenRT,pillip8282/TizenRT,pillip8282/TizenRT,jeongarmy/TizenRT,an4967/TizenRT,junmin-kim/TizenRT,jeongchanKim/TizenRT,jsdosa/TizenRT,junmin-kim/TizenRT,Samsung/TizenRT,junmin-kim/TizenRT