remove all references to isc_socket and related types

Removed socket.c, socket.h, and all references to isc_socket_t,
isc_socketmgr_t, isc_sockevent_t, etc.

lib/isc/netmgr/netmgr.c

@@ -128,6 +128,13 @@ static const isc_statscounter_t unixstatsindex[] = {
 
 static thread_local int isc__nm_tid_v = ISC_NETMGR_TID_UNKNOWN;
 
+/*
+ * Set by the -T dscp option on the command line. If set to a value
+ * other than -1, we check to make sure DSCP values match it, and
+ * assert if not. (Not currently in use.)
+ */
+int isc_dscp_check_value = -1;
+
 static void
 nmsocket_maybe_destroy(isc_nmsocket_t *sock FLARG);
 static void