selftests: forwarding: Suppress grep warnings

Suppress the following grep warnings:

[...]
INFO: # Port group entries configuration tests - (*, G)
TEST: Common port group entries configuration tests (IPv4 (*, G))   [ OK ]
TEST: Common port group entries configuration tests (IPv6 (*, G))   [ OK ]
grep: warning: stray \ before /
grep: warning: stray \ before /
grep: warning: stray \ before /
TEST: IPv4 (*, G) port group entries configuration tests            [ OK ]
grep: warning: stray \ before /
grep: warning: stray \ before /
grep: warning: stray \ before /
TEST: IPv6 (*, G) port group entries configuration tests            [ OK ]
[...]

They do not fail the test, but do clutter the output.

Fixes: b6d00da0 ("selftests: forwarding: Add bridge MDB test")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://lore.kernel.org/r/20240208155529.1199729-4-idosch@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -329,7 +329,7 @@ __cfg_test_port_ip_star_g()
 
 	bridge -d -s mdb get dev br0 grp $grp vid 10 | grep -q " 0.00"
 	check_err $? "(*, G) \"permanent\" entry has a pending group timer"
-	bridge -d -s mdb get dev br0 grp $grp vid 10 | grep -q "\/0.00"
+	bridge -d -s mdb get dev br0 grp $grp vid 10 | grep -q "/0.00"
 	check_err $? "\"permanent\" source entry has a pending source timer"
 
 	bridge mdb del dev br0 port $swp1 grp $grp vid 10
@@ -346,7 +346,7 @@ __cfg_test_port_ip_star_g()
 
 	bridge -d -s mdb get dev br0 grp $grp vid 10 | grep -q " 0.00"
 	check_fail $? "(*, G) EXCLUDE entry does not have a pending group timer"
-	bridge -d -s mdb get dev br0 grp $grp vid 10 | grep -q "\/0.00"
+	bridge -d -s mdb get dev br0 grp $grp vid 10 | grep -q "/0.00"
 	check_err $? "\"blocked\" source entry has a pending source timer"
 
 	bridge mdb del dev br0 port $swp1 grp $grp vid 10
@@ -363,7 +363,7 @@ __cfg_test_port_ip_star_g()
 
 	bridge -d -s mdb get dev br0 grp $grp vid 10 | grep -q " 0.00"
 	check_err $? "(*, G) INCLUDE entry has a pending group timer"
-	bridge -d -s mdb get dev br0 grp $grp vid 10 | grep -q "\/0.00"
+	bridge -d -s mdb get dev br0 grp $grp vid 10 | grep -q "/0.00"
 	check_fail $? "Source entry does not have a pending source timer"
 
 	bridge mdb del dev br0 port $swp1 grp $grp vid 10