res_pjsip.c: Fix Contact header rendering for IPv6 addresses.

Fix suggested by @nvsystems.

Fixes #985

(cherry picked from commit 5c76486203)

res/res_pjsip.c

@@ -1143,9 +1143,9 @@ static pjsip_dialog *create_dialog_uas(const struct ast_sip_endpoint *endpoint,
 	contact.slen = pj_ansi_snprintf(contact.ptr, PJSIP_MAX_URL_SIZE,
 			"<%s:%s%s%s%.*s%s:%d%s%s>",
 			uas_use_sips_contact(rdata) ? "sips" : "sip",
-			(type & PJSIP_TRANSPORT_IPV6) ? "[" : "",
 			S_OR(endpoint->contact_user, ""),
                         (!ast_strlen_zero(endpoint->contact_user)) ? "@" : "",
+			(type & PJSIP_TRANSPORT_IPV6) ? "[" : "",
 			(int)transport->local_name.host.slen,
 			transport->local_name.host.ptr,
 			(type & PJSIP_TRANSPORT_IPV6) ? "]" : "",