net/netlink_compat: Fix a missing check of nla_parse_nested

In tipc_nl_compat_sk_dump(), if nla_parse_nested() fails, it could return
an error. To be consistent with other invocations of the function call,
on error, the fix passes the return value upstream.

Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>