virNetDevBandwidthPlug: Update function description

The comment is describing arguments passed to the function.
However, there's no @ifmac argument. In 955af4d4 it was replaced
with @ifmac_ptr.  Unfortunately, the comment wasn't updated.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/util/virnetdevbandwidth.c

@@ -389,7 +389,7 @@ virNetDevBandwidthEqual(virNetDevBandwidthPtr a,
  * virNetDevBandwidthPlug:
  * @brname: name of the bridge
  * @net_bandwidth: QoS settings on @brname
- * @ifmac: MAC of interface
+ * @ifmac_ptr: MAC of interface
  * @bandwidth: QoS settings for interface
  * @id: unique ID (MUST be greater than 2)
  *