network: Add virNetworkObj Get/Set API's for @dnsmasqPid and @radvdPid

network: Add virNetworkObj Get/Set API's for @dnsmasqPid and @radvdPid

In preparation for making the object private, create/use a couple of API's
to get/set the obj->dnsmasqPid and obj->radvdPid.

NB: Since the pid's can sometimes changed based on intervening functions,
be sure to always fetch the latest value.

Signed-off-by: John Ferlan <jferlan@redhat.com>