ovs-appctl: Fix shadow variable that could cause segfault

ovs-appctl: Fix shadow variable that could cause segfault

The variable "socket_name" contains the name of the unix domain socket
to be used for communicating with the OVS process.  If the target does
not begin with a "/", the socket name is determined based on a pidfile.
A shadow copy of "socket_name" was kept in the block that looks at the
pidfile, which would cause the function-level one to not be set.  This
removes that shadow copy.