[tools] fix build on opensuse 15.3

tickle_tcp.c: In function ‘send_tickle_ack’:
tickle_tcp.c:60:26: error: ‘phdr’ may be used uninitialized in this function [-Werror=maybe-uninitialized]

sum += (uint32_t)ntohs(*data);
                       ^

tickle_tcp.c:60:26: error: ‘*((void *)&phdr+2)’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
tickle_tcp.c:60:26: error: ‘*((void *)&phdr+4)’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
tickle_tcp.c:60:26: error: ‘*((void *)&phdr+6)’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
cc1: all warnings being treated as errors
gmake[3]: *** [Makefile:697: tickle_tcp.o] Error 1

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>