Medium: IPaddr2: add option to enable sending refresh arp packets in monitor

This commit introduces a new parameter:
OCF_RESKEY_arp_count_refresh_default (default: 0)

This parameter allows to specify whether to send gratuitous ARP packets during
the monitoring of the resource, and how many.
This is to alleviate issues with potentially stuck switch ARP caches,
which can arise in case of split brain situations. Example:

• a two node cluster is interconnected directly as well as through a switch. Node A is master, node B is slave
• communication between master and slave is severed (split brain)
• node B initializes the virtual IPs and sends gratuitous ARP packets
• the switch updated its ARP table to point to B
• node B dies (without node A noticing)
• node A never notices anything wrong
• the switch fails to notice that the virtual IP belongs to A