tests: socket: Fix compiler warnings

../src/main.c:662:13: warning: cast from pointer to integer of different
size [-Wpointer-to-int-cast]
  662 |  int sock = (int)p1;
      |             ^
../src/main.c: In function 'spawn_child':
../src/main.c:671:4: warning: cast to pointer from integer of different
size [-Wint-to-pointer-cast]
  671 |    (void *)sock, NULL, NULL, 0, K_USER,

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>