cache_mngr: Return proper error code if nl_socket_alloc() fails

If nl_socket_alloc() failes in nl_cache_mngr_alloc() we would currently
return 0 due to the previous assignment of the err variable, even though
the failed allocation is an error condition. Fix this by setting err to
-NLE_NOMEM if nl_socket_alloc() fails.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Thomas Haller <thaller@redhat.com>
cache_mngr: Fix assignment of error code in nl_cache_mngr_alloc()

In the current form, the parentheses in these two if (...) statements
lead to err being assigned the result of nl_connect(...) < 0 and
nl_socket_set_nonblocking(...) < 0 instead of the return value of these
functions. Adjust the parentheses to assign the returned error code to
err.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Thomas Haller <thaller@redhat.com>