Below patch fixes the following coverity findings

Error: OVERRUN_STATIC:
/libvirt/src/qemu/qemu_command.c:152:
overrun-buffer-val: Overrunning static array "net->mac" of size 6 bytes by passing it as an argument to a function which indexes it at byte position 15.
/libvirt/src/util/virnetdevmacvlan.c:948:
access_dbuff_const: Calling "virNetDevMacVLanVPortProfileRegisterCallback" indexes array "macaddress" at byte position 15.
/libvirt/src/util/virnetdevmacvlan.c:773:
access_dbuff_const: Calling "memcpy" indexes array "macaddress" with index "16UL" at byte position 15.

Error: OVERRUN_STATIC:
/libvirt/src/qemu/qemu_migration.c:2744:
overrun-buffer-val: Overrunning static array "net->mac" of size 6 bytes by passing it as an argument to a function which indexes it at byte position 15.
/libvirt/src/util/virnetdevmacvlan.c:773:
access_dbuff_const: Calling "memcpy" indexes array "macaddress" with index "16UL" at byte position 15.

Error: OVERRUN_STATIC:
/libvirt/src/qemu/qemu_driver.c:435:
overrun-buffer-val: Overrunning static array "net->mac" of size 6 bytes by passing it as an argument to a function which indexes it at byte position 15.
/libvirt/src/util/virnetdevmacvlan.c:1036:
access_dbuff_const: Calling "virNetDevMacVLanVPortProfileRegisterCallback" indexes array "macaddress" at byte position 15.
/libvirt/src/util/virnetdevmacvlan.c:773:
access_dbuff_const: Calling "memcpy" indexes array "macaddress" with index "16UL" at byte position 15.