mwan3: reduce calls to `ip route list'

Signed-off-by: Aaron Goodman <aaronjg@stanford.edu>

net/mwan3/files/lib/mwan3/mwan3.sh

@@ -39,14 +39,16 @@ mwan3_rtmon_ipv4()
 	local tid=1
 	local idx=0
 	local ret=1
+	local tbl=""
 	mkdir -p /tmp/mwan3rtmon
 	($IP4 route list table main  | grep -v "^default\|linkdown" | sort -n; echo empty fixup) >/tmp/mwan3rtmon/ipv4.main
 	while uci get mwan3.@interface[$idx] >/dev/null 2>&1 ; do
 		idx=$((idx+1))
 		tid=$idx
 		[ "$(uci get mwan3.@interface[$((idx-1))].family)" = "ipv4" ] && {
-			if $IP4 route list table $tid | grep -q ^default; then
-				($IP4 route list table $tid  | grep -v "^default\|linkdown" | sort -n; echo empty fixup) >/tmp/mwan3rtmon/ipv4.$tid
+			tbl=$($IP4 route list table $tid)
+			if echo "$tbl" | grep -q ^default; then
+				(echo "$tbl"  | grep -v "^default\|linkdown" | sort -n; echo empty fixup) >/tmp/mwan3rtmon/ipv4.$tid
 				cat /tmp/mwan3rtmon/ipv4.$tid | grep -v -x -F -f /tmp/mwan3rtmon/ipv4.main | while read line; do
 					$IP4 route del table $tid $line
 				done
@@ -70,14 +72,16 @@ mwan3_rtmon_ipv6()
 	local tid=1
 	local idx=0
 	local ret=1
+	local tbl=""
 	mkdir -p /tmp/mwan3rtmon
 	($IP6 route list table main  | grep -v "^default\|^::/0\|^unreachable" | sort -n; echo empty fixup) >/tmp/mwan3rtmon/ipv6.main
 	while uci get mwan3.@interface[$idx] >/dev/null 2>&1 ; do
 		idx=$((idx+1))
 		tid=$idx
 		[ "$(uci get mwan3.@interface[$((idx-1))].family)" = "ipv6" ] && {
-			if $IP6 route list table $tid | grep -q "^default\|^::/0"; then
-				($IP6 route list table $tid  | grep -v "^default\|^::/0\|^unreachable" | sort -n; echo empty fixup) >/tmp/mwan3rtmon/ipv6.$tid
+			tbl=$($IP6 route list table $tid)
+			if echo "$tbl" | grep -q "^default\|^::/0"; then
+				(echo "$tbl"  | grep -v "^default\|^::/0\|^unreachable" | sort -n; echo empty fixup) >/tmp/mwan3rtmon/ipv6.$tid
 				cat /tmp/mwan3rtmon/ipv6.$tid | grep -v -x -F -f /tmp/mwan3rtmon/ipv6.main | while read line; do
 					$IP6 route del table $tid $line
 				done