Makefile: move default goal up

Since commit e6dcf46 there is no need to specify the default goal
explicitly.

The common convention for Makefiles is the first goal in the file
is the default one, so most universally there's "all:" goal
at the beginning. Let's adhere to this convention, moving
the "all:" up where it is to be expected.

[v2: keep the DEFAULT_GOAL for clarity]

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>