qemuNetworkIfaceConnect() used to have a special case for
actualType='network' (a network with forward mode of route, nat, or
isolated) to call the libvirt public API to retrieve the bridge being
used by a network. That is no longer necessary - since all network
types that use a bridge and tap device now get the bridge name stored
in the ActualNetDef, we can just always use
virDomainNetGetActualBridgeName() instead.

(an audit of the two callers to qemuNetworkIfaceConnect() confirms
that it is never called for any other type of network, so the dead
code in the else statement (logging an internal error if it is called
for any other type of network) is eliminated in the process.)