ipa: Partially revert the e1inp_ipa_bts_rsl_connect_n commit

The check was always hit by osmo-bts master leading to the RSL
connection never being made. This is because the type of the line
will be set _after_ the RSL connection has been made. E.g. inside
osmo-bts/src/common/abis.c:

static struct e1inp_sign_link *sign_link_up(void *unit, struct e1inp_line *line,
                                            enum e1inp_sign_type type)
{
        struct e1inp_sign_link *sign_link = NULL;

        switch (type) {
	...
        case E1INP_SIGN_RSL:
                LOGP(DABIS, LOGL_INFO, "RSL Signalling link up\n");
                e1inp_ts_config_sign(&line->ts[E1INP_SIGN_RSL-1], line);
	...

Only the call to e1inp_ts_config_sign will set the type to be
E1INP_TS_TYPE_SIGN. Before the call the type is still _NONE and
the connect was rejected.
diff --git a/src/input/ipaccess.c b/src/input/ipaccess.c
index 145e471..8ffdb19 100644
--- a/src/input/ipaccess.c
+++ b/src/input/ipaccess.c
@@ -915,12 +915,6 @@
 			"trx_nr (%d) out of range\n", trx_nr);
 		return -EINVAL;
 	}
-	if (line->ts[E1INP_SIGN_RSL+trx_nr-1].type != E1INP_TS_TYPE_SIGN) {
-		LOGP(DLINP, LOGL_ERROR, "cannot create RSL BTS link: "
-			"trx_nr (%d) does not refer to a signalling link\n",
-			trx_nr);
-		return -EINVAL;
-	}
 
 	rsl_link = ipa_client_conn_create(tall_ipa_ctx,
 					  &line->ts[E1INP_SIGN_RSL+trx_nr-1],