ipaddress: fix ipaddr_flush for Linux >= 3.1

ipaddress: fix ipaddr_flush for Linux >= 3.1

Linux version 3.1 introduced a consistency check for netlink dumps in
commit 670dc28 ("netlink: advertise incomplete dumps"). This bites
iproute2 when flushing more addresses than can fit into a single
RTM_GETADDR response. To silence the spurious error message "Dump was
interrupted and may be inconsistent.", advise rtnl_dump_filter_l() to
not care about NLM_F_DUMP_INTR.

Signed-off-by: Phil Sutter <phil@nwl.cc>