sysctl.conf: Allow inet free binds

Allow inet free binds (bind to any ip address) so that services which
bind to specific ip addresses (e.g. $MX_IPADDR) don't need to wait for
network setup.

This simplifies our startup, because we can avoid to pull
network-online.target or order units after network.service just to to be
able to listen to a specific address.

Note, that we still need network to resolve names to addresses.

misc_etc_files/sysctl.conf

@@ -45,3 +45,9 @@ kernel.shmall = 34359738368
 # user request: Allow CPU event access by users without CAP_SYS_ADMIN
 
 kernel.perf_event_paranoid = -1
+
+# allow inet free binds (bind to any ip address) so that services which bind to
+# specific ip addresses (e.g. $MX_IPADDR) don't need to wait for network setup
+
+net.ipv4.ip_nonlocal_bind = 1
+net.ipv6.ip_nonlocal_bind = 1