> Description of problem:
Request to add MemAvailable support on Linux for snmp

> Version-Release number of selected component (if applicable):
net-snmp-5.8-22.el8

> How reproducible:
Always

> Steps to Reproduce:
1. Install the latest version of net-snmp on RHEL8

2. Configure snmpd:
-------------8< -------------8< -------------8< -------------
[root@rhel8 ~]# cat /etc/snmp/snmpd.conf
com2sec notConfigUser default public
group notConfigGroup v1 notConfigUser
group notConfigGroup v2c notConfigUser
view all included .1 80
access notConfigGroup "" any noauth exact all none none
syslocation Unknown (edit /etc/snmp/snmpd.conf)
syscontact Root <root@localhost> (configure /etc/snmp/snmp.local.conf)
dontLogTCPWrappersConnects yes

[root@rhel8 ~]# systemctl restart snmpd
-------------8< -------------8< -------------8< -------------

3. Get .1.3.6.1.4.1.2021.4.27:
-------------8< -------------8< -------------8< -------------
[root@rhel8 ~]# snmpwalk -v2c -c public localhost .1.3.6.1.4.1.2021.4.27
UCD-SNMP-MIB::memory.27 = No Such Object available on this agent at this OID
-------------8< -------------8< -------------8< -------------

> Actual results:
OID not found, no result available.

> Expected results:
OID found and return the value of MemAvailable.

> Additional info:

Upstream has implemented via:

• https://github.com/net-snmp/net-snmp/commit/5b8bf5d4130761c3374f9ad618e8a76bb75eb634#diff-a06d7fdd13c0aa8ea45f55a6b9cbf6de34682d0422872cba5dae272f3ed0bc5b