osmo_io: rename unsupported SCTP mode to OSMO_IO_FD_MODE_SCTP_RECVMSG_SEND

The two functions of the SCTP socket interface we use in osmo-* are
sctp_send() and sctp_recvmsg().  We do not use sctp_sendmsg() at all,
so let's make sure the mode is named correctly.

Change-Id: Ie2d1c7ce6f211dbe025a0e843ad733443102ea15
Related: OS#5751
diff --git a/src/core/osmo_io.c b/src/core/osmo_io.c
index 649bf73..1a8c01d 100644
--- a/src/core/osmo_io.c
+++ b/src/core/osmo_io.c
@@ -337,7 +337,7 @@
 	case OSMO_IO_FD_MODE_RECVFROM_SENDTO:
 		iofd->io_ops.recvfrom_cb(iofd, rc, msg, &hdr->osa);
 		break;
-	case OSMO_IO_FD_MODE_SCTP_RECVMSG_SENDMSG:
+	case OSMO_IO_FD_MODE_SCTP_RECVMSG_SEND:
 		/* TODO Implement */
 		OSMO_ASSERT(false);
 		break;
@@ -688,7 +688,7 @@
 		else
 			osmo_iofd_ops.read_disable(iofd);
 		break;
-	case OSMO_IO_FD_MODE_SCTP_RECVMSG_SENDMSG:
+	case OSMO_IO_FD_MODE_SCTP_RECVMSG_SEND:
 	default:
 		OSMO_ASSERT(0);
 	}