Support for multiple RSL connections with ABIS/ipaccess (BTS side)

In order to support multiple TRX, multiple RSL connections can be
establised. e1inp_ipa_bts_rsl_connect() requires an additional parameter
to set the TRX number.

The ts[] array (member of struct e1inp_line) refers to OML and RSL.
ts[0] refers to OML link, ts[1] to RSL link of first TRX, ts[2] to
RSL link of second TRX (if exists) and so on.

The code was successfully tested with osmobts-trx and UmTRX with two
transceivers.

The user of e1inp_ipa_bts_rsl_connect() (which is osmo-bts) can use
the new function like this (backwards compatibility function provided):

src/common/oml.c
-	rc = e1inp_ipa_bts_rsl_connect(oml_link->ts->line, inet_ntoa(in), port);
+	rc = e1inp_ipa_bts_rsl_connect_n(oml_link->ts->line, inet_ntoa(in), port,
+		trx->nr);
diff --git a/tests/e1inp_ipa_bts_test.c b/tests/e1inp_ipa_bts_test.c
index 18f1709..5798d00 100644
--- a/tests/e1inp_ipa_bts_test.c
+++ b/tests/e1inp_ipa_bts_test.c
@@ -71,7 +71,7 @@
 			/* Now we can send OML messages to the BSC. */
 			bts_state = BTS_TEST_OML_SIGN_LINK_UP;
 		}
-		e1inp_ipa_bts_rsl_connect(line, "127.0.0.1", IPA_TCP_PORT_RSL);
+		e1inp_ipa_bts_rsl_connect(line, "127.0.0.1", IPA_TCP_PORT_RSL, 0);
 		break;
 	case E1INP_SIGN_RSL:
 		LOGP(DBTSTEST, LOGL_NOTICE, "RSL link up request received.\n");