syscalls/sockioctl: Align buffer to struct ifreq

In setup3, the following line can lead to an undefined behavior:
  ifr = *(struct ifreq *)ifc.ifc_buf;

Indeed, at this point it can be assumed that ifc.ifc_buf is suitably
aligned for struct ifreq.
However, ifc.ifc_buf is assigned to buf which has no alignment
constraints. This means there exists cases where buf is not suitably
aligned to load a struct ifreq, which can generate a SIGBUS.

Force the alignment of buf to that of struct ifreq.

Signed-off-by: Teo Couprie Diaz <teo.coupriediaz@arm.com>

testcases/kernel/syscalls/sockioctl/sockioctl01.c

@@ -52,7 +52,13 @@ static struct ifreq ifr;
 static int sinlen;
 static int optval;
 
-static char buf[8192];
+/*
+ * buf has no alignment constraints by default. However, it is used to load
+ * a struct ifreq in setup3, which requires it to have an appropriate alignment
+ * to prevent a possible undefined behavior.
+ */
+static char buf[8192]
+	__attribute__((aligned(__alignof__(struct ifreq))));
 
 static void setup(void);
 static void setup0(void);