bonding: remove test for IP in ARP monitor

	Remove bond_has_ip and all references to it.  With this change,
the ARP monitor will always send ARP probes if the master is up and has
at least one slave.  If the bond has an IP address, it is used in the
ARP probe; if not, the probes are sent with all zeros in the sender's
IP address (which is consistent with an RFC 2131 4.4.1 duplicate address
probe).

	This is useful for cases when bonding itself is hidden underneath
a layer of virtual devices, e.g., with Xen.

	Change suggested by Tsutomu Fujii <t-fujii@nb.jp.nec.com>, who
included a one-line patch that only affected active-backup mode.

Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>