virnetsocket: fix getsockopt on FreeBSD

aa0f0992 introduced a strict error checking for getsockopt and it
revealed that getting a peer credential of a socket on FreeBSD
didn't work. Libvirtd hits the error:
  error : virNetSocketGetUNIXIdentity:1198 : Failed to get valid
  client socket identity groups

SOL_SOCKET (0xffff) was used as a level of getsockopt for
LOCAL_PEERCRED, however, it was wrong. 0 is correct as well as
Mac OS X.

So for LOCAL_PEERCRED our options are SOL_LOCAL (if defined) or
0 on Mac OS X and FreeBSD. According to the fact, the patch
simplifies the code by removing ifdef __APPLE__.

I tested the patch on FreeBSD 8.4, 9.2 and 10.0-BETA1.
Signed-off-by: NRyota Ozaki <ozaki.ryota@gmail.com>

src/rpc/virnetsocket.c

@@ -1152,19 +1152,18 @@ cleanup:
 /* VIR_SOL_PEERCRED - the value needed to let getsockopt() work with
  * LOCAL_PEERCRED
  */
-# ifdef __APPLE__
+
+/* Mac OS X 10.8 provides SOL_LOCAL for LOCAL_PEERCRED */
 # ifdef SOL_LOCAL
 #  define VIR_SOL_PEERCRED SOL_LOCAL
 # else
-/* Prior to Mac OS X 10.7, SOL_LOCAL was not defined and users were
- * expected to supply 0 as the second value for getsockopt() when using
- * LOCAL_PEERCRED
+/* FreeBSD and Mac OS X prior to 10.7, SOL_LOCAL is not defined and
+ * users are expected to supply 0 as the second value for getsockopt()
+ * when using LOCAL_PEERCRED. NB SOL_SOCKET cannot be used instead
+ * of SOL_LOCAL
  */
 #  define VIR_SOL_PEERCRED 0
 # endif
-# else
-#  define VIR_SOL_PEERCRED SOL_SOCKET
-# endif
 
 int virNetSocketGetUNIXIdentity(virNetSocketPtr sock,
                                 uid_t *uid,