e1_input: change prototype of ->sign_link(...)

This patch removes the struct e1inp_sign_link parameter since this
is already available in the msgb->dst field of the message.
diff --git a/tests/e1inp_ipa_bts_test.c b/tests/e1inp_ipa_bts_test.c
index 8ba49c5..bd67a83 100644
--- a/tests/e1inp_ipa_bts_test.c
+++ b/tests/e1inp_ipa_bts_test.c
@@ -77,7 +77,7 @@
 	e1inp_sign_link_destroy(rsl_sign_link);
 }
 
-static int sign_link(struct msgb *msg, struct e1inp_sign_link *link)
+static int sign_link(struct msgb *msg)
 {
 	LOGP(DBTSTEST, LOGL_NOTICE, "OML/RSL message received.\n");
 	return 0;