[psud]: Fix for psud crash because of database connection reset (#3647)

When database service is down, psud daemon throws an error because of DB connection reset, this because pmon service has no dependency with database service.

To resolve this issue, added database service dependency to the pmon service.

Also, increased the net.core.somaxconn value to 512 to solve the connection failure on the scaled setup.

build_debian.sh

@@ -392,6 +392,9 @@ set /files/etc/sysctl.conf/net.ipv4.udp_l3mdev_accept 1
 
 set /files/etc/sysctl.conf/net.core.rmem_max 2097152
 set /files/etc/sysctl.conf/net.core.wmem_max 2097152
+
+set /files/etc/sysctl.conf/net.core.somaxconn 512
+
 " -r $FILESYSTEM_ROOT
 
 if [[ $CONFIGURED_ARCH == amd64 ]]; then

files/build_templates/pmon.service.j2

@@ -1,7 +1,7 @@
 [Unit]
 Description=Platform monitor container
-Requires=updategraph.service
-After=updategraph.service
+Requires=database.service updategraph.service
+After=database.service updategraph.service
 {% if sonic_asic_platform == 'mellanox' %}
 After=syncd.service
 {% endif %}