maint: avoid static zero init in helpers
    
    C guarantees that static variables are zero-initialized.  Some older
    compilers (and also gcc -fno-zero-initialized-in-bss) create larger
    binaries if you explicitly zero-initialize a static variable.
    
    * src/conf/nwfilter_conf.c: Fix initialization.
    * src/cpu/cpu_x86.c: Likewise.
    * src/interface/interface_backend_netcf.c: Likewise.
    * src/locking/lock_daemon.c: Likewise.
    * src/locking/lock_driver_lockd.c: Likewise.
    * src/locking/lock_driver_sanlock.c: Likewise.
    * src/network/bridge_driver.c: Likewise.
    * src/node_device/node_device_udev.c: Likewise.
    * src/nwfilter/nwfilter_learnipaddr.c: Likewise.
    * src/rpc/virnetserver.c: Likewise.
    * src/security/security_selinux.c
    (virSecuritySELinuxGenSecurityLabel): Likewise.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>