rtpulpfec: fix unconditional use of __attribute__ ((packed))

Fix compilation with MSVC. We still assume that attribute
is supported by all other relevant compilers, which seems
to be the case since we haven't had any complaints about
similar code in rtpsbcpay.
diff --git a/gst/rtp/rtpulpfeccommon.h b/gst/rtp/rtpulpfeccommon.h
index 6735831..2c9d798 100644
--- a/gst/rtp/rtpulpfeccommon.h
+++ b/gst/rtp/rtpulpfeccommon.h
@@ -48,6 +48,14 @@
   GstRTPBuffer rtp;
 } RtpUlpFecMapInfo;
 
+/* FIXME: parse/write these properly instead of relying in packed structs */
+#ifdef _MSC_VER
+#pragma pack(push, 1)
+#define ATTRIBUTE_PACKED
+#else
+#define ATTRIBUTE_PACKED __attribute__ ((packed))
+#endif
+
 /* RFC 5109 */
 /*
     0                   1                   2                   3
@@ -76,7 +84,7 @@
   guint16 seq;
   guint32 timestamp;
   guint16 len;
-} __attribute__ ((packed)) RtpUlpFecHeader;
+} ATTRIBUTE_PACKED RtpUlpFecHeader;
 #else
 typedef struct {
   guint8 E:1;
@@ -91,7 +99,7 @@
   guint16 seq;
   guint32 timestamp;
   guint16 len;
-} __attribute__ ((packed)) RtpUlpFecHeader;
+} ATTRIBUTE_PACKED RtpUlpFecHeader;
 #endif
 
 /*
@@ -110,7 +118,13 @@
   guint16 protection_len;
   guint16 mask;
   guint32 mask_continued;
-} __attribute__ ((packed)) RtpUlpFecLevelHeader;
+} ATTRIBUTE_PACKED RtpUlpFecLevelHeader;
+
+#ifdef _MSC_VER
+#pragma pack(pop)
+#else
+#undef ATTRIBUTE_PACKED
+#endif
 
 gboolean          rtp_ulpfec_map_info_map                  (GstBuffer *buffer, RtpUlpFecMapInfo *info);
 void              rtp_ulpfec_map_info_unmap                (RtpUlpFecMapInfo *info);