tipc: remove the unnecessary msg->req check from tipc_nl_compat_bearer_set

tipc_nl_compat_bearer_set() is only called by tipc_nl_compat_link_set()
which already does the check for msg->req check, so remove it from
tipc_nl_compat_bearer_set(), and do the same in tipc_nl_compat_media_set().

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>