[SELinux]: Fix double free in selinux_netlbl_sock_setsid()

As pointed out by Adrian Bunk, commit
45c950e0 ("fix memory leak in netlabel
code") caused a double-free when security_netlbl_sid_to_secattr()
fails.  This patch fixes this by removing the netlbl_secattr_destroy()
call from that function since we are already releasing the secattr
memory in selinux_netlbl_sock_setsid().

Signed-off-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>