selftests: mlxsw: Fix test failure on Spectrum-4

Remove assumptions about shared buffer cell size and instead query the
cell size from devlink. Adjust the test to send small packets that fit
inside a single cell.

Tested on Spectrum-{1,2,3,4}.

Fixes: 47354021 ("mlxsw: spectrum: Extend to support Spectrum-4 ASIC")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/f7dfbf3c4d1cb23838d9eb99bab09afaa320c4ca.1692268427.git.petrm@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/mlxsw/sharedbuffer.sh

@@ -98,12 +98,12 @@ sb_occ_etc_check()
 
 port_pool_test()
 {
-	local exp_max_occ=288
+	local exp_max_occ=$(devlink_cell_size_get)
 	local max_occ
 
 	devlink sb occupancy clearmax $DEVLINK_DEV
 
-	$MZ $h1 -c 1 -p 160 -a $h1mac -b $h2mac -A 192.0.1.1 -B 192.0.1.2 \
+	$MZ $h1 -c 1 -p 10 -a $h1mac -b $h2mac -A 192.0.1.1 -B 192.0.1.2 \
 		-t ip -q
 
 	devlink sb occupancy snapshot $DEVLINK_DEV
@@ -126,12 +126,12 @@ port_pool_test()
 
 port_tc_ip_test()
 {
-	local exp_max_occ=288
+	local exp_max_occ=$(devlink_cell_size_get)
 	local max_occ
 
 	devlink sb occupancy clearmax $DEVLINK_DEV
 
-	$MZ $h1 -c 1 -p 160 -a $h1mac -b $h2mac -A 192.0.1.1 -B 192.0.1.2 \
+	$MZ $h1 -c 1 -p 10 -a $h1mac -b $h2mac -A 192.0.1.1 -B 192.0.1.2 \
 		-t ip -q
 
 	devlink sb occupancy snapshot $DEVLINK_DEV
@@ -154,16 +154,12 @@ port_tc_ip_test()
 
 port_tc_arp_test()
 {
-	local exp_max_occ=96
+	local exp_max_occ=$(devlink_cell_size_get)
 	local max_occ
 
-	if [[ $MLXSW_CHIP != "mlxsw_spectrum" ]]; then
-		exp_max_occ=144
-	fi
-
 	devlink sb occupancy clearmax $DEVLINK_DEV
 
-	$MZ $h1 -c 1 -p 160 -a $h1mac -A 192.0.1.1 -t arp -q
+	$MZ $h1 -c 1 -p 10 -a $h1mac -A 192.0.1.1 -t arp -q
 
 	devlink sb occupancy snapshot $DEVLINK_DEV