Fix a bug in single socket connection to Wifi Supplicant

My change to post messages without IFACE=<iface> prefix to all interfaces
was correct; but messages sent with IFACE=p2p-p2p0-0 et al were being sent
to p2p monitor only. This change mimics that to resolve some issues
introduced by the single socket change.

Bug: 10257602
Change-Id: Ia6164cb3cfd11c2a0a7b011eceaeabfd9677f62c