Linux PMDA: add a bunch of new TcpExt metrics from /proc/net/netstat

Appeared recently on F39.

Specifically below network.tcp in the PMNS:
   tcpaorequired      60:53:212
   tcpaobad           60:53:213
   tcpaokeynotfound   60:53:214
   tcpaogood          60:53:215
   tcpaodroppedicmps  60:53:216

Update add_netstat_field helper script ... this is ALL automated now.

Extend QA test and /proc/net/* test data in QA.  Extend and remake qa/1805.

qa/1805

@@ -1,6 +1,6 @@
 #!/bin/sh
 # PCP QA Test No. 1805
-# Exercise Linux /proc/net/netstat MPTCP metrics
+# Exercise Linux /proc/net/netstat MPTCP and TCP metrics
 #
 # Copyright (c) 2020 Red Hat.  All Rights Reserved.
 #
@@ -39,10 +39,15 @@ pmda=$PCP_PMDAS_DIR/linux/pmda_linux.so,linux_init
 rm -fr $root
 mkdir -p $root/proc/net || _fail "root in use when processing $file"
 cp $here/linux/proc_net_netstat $root/proc/net/netstat
+cp $here/linux/proc_net_snmp $root/proc/net/snmp
 
 echo "== Checking network.mptcp metrics"
 pminfo -f -L -K clear -K add,60,$pmda network.mptcp
 
+echo
+echo "== Checking network.tcp metrics"
+pminfo -f -L -K clear -K add,60,$pmda network.tcp
+
 # success, all done
 status=0
 exit