Fix Rig.set_freq()

This is also swapping the arguments to make the vfo optional
like in other methods.

bindings/python/test_startup.py

@@ -33,7 +33,7 @@ class TestClass:
         assert my_rig.error_status == Hamlib.RIG_OK
         assert Hamlib.rigerror(my_rig.error_status) == "Command completed successfully\n"
 
-        assert my_rig.set_freq(Hamlib.RIG_VFO_B, 5700000000) is None
+        assert my_rig.set_freq(5700000000, Hamlib.RIG_VFO_B) is None
         assert my_rig.set_vfo(Hamlib.RIG_VFO_B) is None
         assert my_rig.get_freq() == 5700000000
 

bindings/rig.swg

@@ -363,7 +363,7 @@ typedef channel_t * const_channel_t_p;
 #define _VFO_ARG	,vfo
 #define _VFO_DECL	,vfo_t vfo = RIG_VFO_CURR
 
-	METHOD3(set_freq, freq_t)
+	METHOD1(set_freq, freq_t)
 	METHOD2_INIT(set_mode, rmode_t, pbwidth_t, RIG_PASSBAND_NORMAL)
 	METHOD3(set_ptt, ptt_t)
 	METHOD3(set_rptr_shift, rptr_shift_t)