Add var to suppress `Privacy: none` header

Apparently the MetaSwitch guys incorrectly interpret `Privacy: none`
as `Privacy: id`.

ref: RFC 3325
Reported-by: Stéphane Alnet <stephane@shimaore.net>

FS-6817 #resolve

src/mod/endpoints/mod_sofia/sofia_glue.c

@@ -1075,7 +1075,9 @@ switch_status_t sofia_glue_do_invite(switch_core_session_t *session)
 			if (switch_test_flag(caller_profile, SWITCH_CPF_HIDE_NUMBER)) {
 				tech_pvt->privacy = "id";
 			} else {
-				tech_pvt->privacy = "none";
+				if (!(val = switch_channel_get_variable(channel, "sip_cid_suppress_privacy_none")) || !switch_true(val)) {
+					tech_pvt->privacy = "none";
+				}
 			}
 
 			break;