check_mikrotik_sw_fw updates

check_mikrotik_sw_fw.patch

# diff -u check_mikrotik_sw_fw check_mikrotik_sw_fw.new
--- check_mikrotik_sw_fw        2019-09-05 16:12:12.843534466 +0200
+++ check_mikrotik_sw_fw.new    2019-09-19 22:38:11.560855856 +0200
@@ -24,8 +24,19 @@
       ;;
   esac
 done
-FW=$(snmpwalk -Ov -On -Oq -Cc -c $COMMUNITY -v $VERSION $HOST .1.3.6.1.4.1.14988.1.1.7.4.0)
-SW=$(snmpwalk -Ov -On -Oq -Cc -c $COMMUNITY -v $VERSION $HOST .1.3.6.1.4.1.14988.1.1.4.4.0)
+
+FW=$(snmpget -Ov -Oq -c $COMMUNITY -v $VERSION $HOST .1.3.6.1.4.1.14988.1.1.7.4.0 2>&1)
+if [ $? -ne 0 ]; then
+    echo "UNKNOWN: ${FW}"
+    exit 3
+fi
+
+SW=$(snmpget -Ov -Oq -c $COMMUNITY -v $VERSION $HOST .1.3.6.1.4.1.14988.1.1.4.4.0 2>&1)
+if [ $? -ne 0 ]; then
+    echo "UNKNOWN: ${SW}"
+    exit 3
+fi
+
 if [ "$FW" == "$SW" ]; then
   echo "OK: Software and firmware versions match ($SW)"
   exit 0

• check exit status from snmp command and return "UNKNOWN" if it failed
• use snmpget instead of snmpwalk since a specific OID is being queried, we don't need to walk anything
• don't use -On, unnecessary since OID is being suppressed anyway by -Ov