This is typically used to mount Docker containers but it generates too
many volatile metrics which aren't useful.

Change-Id: I00117895570515b2c8f9690542e83061309464c3

Change-Id: Id4b0b405872457bd8b20f450e4031d6808d3cf59

Change-Id: Ic39fa0f18e0d9aeca0ef73ae6d985d12d15a1c3a

This is to comply to a comment from @cznewt in
https://github.com/tcpcloud/salt-formula-heka/pull/24.

This patch replaces the "interface" collectd plugin by the "netlink" one. The
"netlink" plugin provides the same metrics as "interface" but plus other
metrics such as the number of dropped packets.