ifevent: increase netlink socket recv buffer size

We saw that when setting up multiple bondings, our netlink socket receive
queue filled up before we could process it, generating the following:

netlink receive error: No buffer space available

and preventing the interfaces from being configured properly. Increasing
the receive buffer size on the netlink socket fixes this.
Merge pull request #386 from kmroz/nl-bufsize

ifevent: increase netlink socket recv buffer size