maint: avoid static zero init in helpers

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>