socket: enable only specified IP families

Allow an IP family to be specified in the socket initialization in order
to globally disable the other family. This replaces the ntp_io and
cmdmon code handling the -4/-6 options and fixes a case where the NTP
client could still use a disabled family if the source was specified
with an IP address.

main.c

@@ -568,11 +568,11 @@ int main
   SRC_Initialise();
   RCL_Initialise();
   KEY_Initialise();
-  SCK_Initialise();
+  SCK_Initialise(address_family);
 
   /* Open privileged ports before dropping root */
-  CAM_Initialise(address_family);
-  NIO_Initialise(address_family);
+  CAM_Initialise();
+  NIO_Initialise();
   NCR_Initialise();
   CNF_SetupAccessRestrictions();