soreuseport: Fix reuseport_bpf testcase on 32bit architectures

This fixes the following compiler warnings when compiling the
reuseport_bpf testcase on a 32 bit platform:

reuseport_bpf.c: In function ‘attach_ebpf’:
reuseport_bpf.c:114:15: warning: cast from pointer to integer of ifferent size [-Wpointer-to-int-cast]

Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>