selftests: forwarding: Remove duplicated lib.sh content

commit 25ae948b4478 ("selftests/net: add lib.sh") added net/lib.sh to
contain code shared by tests under net/ and net/forwarding/. However, this
caused issues with selftests from directories other than net/forwarding/,
in particular those under drivers/net/. Those issues were avoided in a
simple way by duplicating some content in commit 2114e83381d3 ("selftests:
forwarding: Avoid failures to source net/lib.sh").

In order to remove the duplicated content, restore the inclusion of
net/lib.sh from net/forwarding/lib.sh but with the following changes:

* net/lib.sh is imported through the net_forwarding_dir path
The original expression "source ../lib.sh" would look for lib.sh in the
directory above the script file's one, which did not work for tests under
drivers/net/.

* net/lib.sh is added to TEST_INCLUDES
Since net/forwarding/lib.sh now sources net/lib.sh, both of those files
must be exported along with tests which source net/forwarding/lib.sh.

Suggested-by: Hangbin Liu <[e-mail]>
Reviewed-by: Hangbin Liu <[e-mail]>
Signed-off-by: Petr Machata <[e-mail]>
Signed-off-by: Benjamin Poirier <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

tools/testing/selftests/drivers/net/bonding/Makefile

···
 	bond_topo_3d1c.sh
 
 TEST_INCLUDES := \
-	../../../net/forwarding/lib.sh
+	../../../net/forwarding/lib.sh \
+	../../../net/lib.sh
 
 include ../../../lib.mk

tools/testing/selftests/drivers/net/dsa/Makefile

···
 	../../../net/forwarding/local_termination.sh \
 	../../../net/forwarding/no_forwarding.sh \
 	../../../net/forwarding/tc_actions.sh \
-	../../../net/forwarding/tc_common.sh
+	../../../net/forwarding/tc_common.sh \
+	../../../net/lib.sh
 
 include ../../../lib.mk

tools/testing/selftests/drivers/net/team/Makefile

···
 
 TEST_INCLUDES := \
 	../bonding/lag_lib.sh \
-	../../../net/forwarding/lib.sh
+	../../../net/forwarding/lib.sh \
+	../../../net/lib.sh
 
 include ../../../lib.mk

tools/testing/selftests/net/forwarding/Makefile

···
 	sch_tbf_etsprio.sh \
 	tc_common.sh
 
+TEST_INCLUDES := \
+	../lib.sh
+
 include ../../lib.mk

tools/testing/selftests/net/forwarding/lib.sh

···
 	source "$net_forwarding_dir/forwarding.config"
 fi
 
-# Kselftest framework requirement - SKIP code is 4.
-ksft_skip=4
-
-busywait()
-{
-	local timeout=$1; shift
-
-	local start_time="$(date -u +%s%3N)"
-	while true
-	do
-		local out
-		out=$("$@")
-		local ret=$?
-		if ((!ret)); then
-			echo -n "$out"
-			return 0
-		fi
-
-		local current_time="$(date -u +%s%3N)"
-		if ((current_time - start_time > timeout)); then
-			echo -n "$out"
-			return 1
-		fi
-	done
-}
+source "$net_forwarding_dir/../lib.sh"
 
 ##############################################################################
 # Sanity checks