set PMTU starting value to 1024 according to RFC4821

sysctl.conf

@@ -3,7 +3,7 @@
 # Contributor: IceCodeNew
 # Contributor: HorlogeSkynet
 # Date Created: October 5, 2020
-# Last Updated: October 12, 2021
+# Last Updated: October 15, 2021
 
 # Licensed under the GNU General Public License Version 3 (GNU GPL v3),
 #   available at: https://www.gnu.org/licenses/gpl-3.0.txt
@@ -232,6 +232,7 @@ net.ipv4.tcp_slow_start_after_idle = 0
 # enabling MTU probing helps mitigating PMTU blackhole issues
 # this may not be desirable on congested networks
 net.ipv4.tcp_mtu_probing = 1
+net.ipv4.tcp_base_mss = 1024
 
 # increase memory thresholds to prevent packet dropping
 net.ipv4.tcp_rmem = 4096 87380 8388608