android/client: Fix compilation with GCC 8

  CC       android/client/android_haltest-if-gatt.o
android/client/if-gatt.c: In function ‘multi_adv_set_inst_data_p’:
android/client/if-gatt.c:2034:7: error: ‘set_scan_rsp’ may be used
      uninitialized in this function [-Werror=maybe-uninitialized]
  EXEC(if_gatt->client->multi_adv_set_inst_data, client_if, set_scan_rsp,
       ^~~~~~~
android/client/if-gatt.c:2034:7: error: ‘include_name’ may be used
         uninitialized in this function [-Werror=maybe-uninitialized]
android/client/if-gatt.c:2034:7: error: ‘include_txpower’ may be used
         uninitialized in this function [-Werror=maybe-uninitialized]
android/client/if-gatt.c: In function ‘set_adv_data_p’:
android/client/if-gatt.c:1859:7: error: ‘set_scan_rsp’ may be used
         uninitialized in this function [-Werror=maybe-uninitialized]
  EXEC(if_gatt->client->set_adv_data, client_if, set_scan_rsp,
       ^~~~~~~
android/client/if-gatt.c:1859:7: error: ‘include_name’ may be used
         uninitialized in this function [-Werror=maybe-uninitialized]
android/client/if-gatt.c:1859:7: error: ‘include_txpower’ may be used
         uninitialized in this function [-Werror=maybe-uninitialized]
cc1: all warnings being treated as errors
make[1]: *** [Makefile:6431: android/client/android_haltest-if-gatt.o] Error 1
make: *** [Makefile:3262: all] Error 2
1 file changed