[kernel]: Increasing gc threshold values for kernel neighbors (sonic-…

…net#4100)

Increase gc threashold values as below:

Previous:

net.ipv6.neigh.default.gc_thresh1=128
net.ipv6.neigh.default.gc_thresh2=512
net.ipv6.neigh.default.gc_thresh3=1024
net.ipv4.neigh.default.gc_thresh1=128
net.ipv4.neigh.default.gc_thresh2=512
net.ipv4.neigh.default.gc_thresh3=1024

New

net.ipv6.neigh.default.gc_thresh1=1024
net.ipv6.neigh.default.gc_thresh2=2048
net.ipv6.neigh.default.gc_thresh3=4096
net.ipv4.neigh.default.gc_thresh1=1024
net.ipv4.neigh.default.gc_thresh2=2048
net.ipv4.neigh.default.gc_thresh3=4096

build_debian.sh

@@ -375,6 +375,12 @@ set /files/etc/sysctl.conf/net.ipv4.conf.all.arp_ignore 2
 
 set /files/etc/sysctl.conf/net.ipv4.neigh.default.base_reachable_time_ms 1800000
 set /files/etc/sysctl.conf/net.ipv6.neigh.default.base_reachable_time_ms 1800000
+set /files/etc/sysctl.conf/net.ipv4.neigh.default.gc_thresh1 1024
+set /files/etc/sysctl.conf/net.ipv6.neigh.default.gc_thresh1 1024
+set /files/etc/sysctl.conf/net.ipv4.neigh.default.gc_thresh2 2048
+set /files/etc/sysctl.conf/net.ipv6.neigh.default.gc_thresh2 2048
+set /files/etc/sysctl.conf/net.ipv4.neigh.default.gc_thresh3 4096
+set /files/etc/sysctl.conf/net.ipv6.neigh.default.gc_thresh3 4096
 
 set /files/etc/sysctl.conf/net.ipv6.conf.default.forwarding 1
 set /files/etc/sysctl.conf/net.ipv6.conf.all.forwarding 1