wifi: don't use :1 bitfield for gboolean type

gboolean is a typedef for "int".

While older compilers might treat such bitfields as unsigned ([1]),
commonly such a bitfield is signed and can only contain the values 0
and -1.

We only want to use numeric 1 for TRUE, hence, creating such bitfields
is wrong, or at least error prone.

In fact, in this case it's a bug, because later we compare
it with a regular gboolean

  if (priv->scanning != new_scanning)

[1] https://lgtm.com/rules/1506024027114/

Fixes: e0f9677018

src/supplicant/nm-supplicant-interface.c

@@ -111,7 +111,7 @@ typedef struct {
 	NMSupplicantInterfaceState state;
 	int            disconnect_reason;
 
-	gboolean       scanning:1;
+	bool           scanning:1;
 
 	bool           scan_done_pending:1;
 	bool           scan_done_success:1;