Merge branch 'mptcp-netlink'

Mat Martineau says:

====================
mptcp: More specific netlink command errors

This series makes the error reporting for the MPTCP_PM_CMD_ADD_ADDR netlink
command more specific, since there are multiple reasons the command could
fail.

Note that patch 2 adds a GENL_SET_ERR_MSG_FMT() macro to genetlink.h,
which is outside the MPTCP subsystem.

Patch 1 refactors in-kernel listening socket and endpoint creation to
simplify the second patch.

Patch 2 updates the error values returned by the in-kernel path manager
when it fails to create a local endpoint.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>