netinet/tcp.h autoconf test is missing u_int32_t on cygwin

I think we need to add sys/types.h on Cygwin, and maybe BSD/macOS as well. But if this configure test is only for KIST, and KIST only works on Linux, maybe we don't need to fix this issue.

configure:9774: checking for struct tcp_info.tcpi_unacked
configure:9774: gcc -c -g -O2   -I${top_srcdir}/src/common conftest.c >&5
In file included from conftest.c:77:
/usr/include/netinet/tcp.h:42:9: error: unknown type name 'u_int32_t'
 typedef u_int32_t tcp_seq;
         ^~~~~~~~~

(similar errors)

configure:9774: $? = 1
configure: failed program was:
| /* confdefs.h */
| #define PACKAGE_NAME "tor"
| #define PACKAGE_TARNAME "tor"
| #define PACKAGE_VERSION "0.3.3.7"

(similar macros)

| #define STDC_HEADERS 1
| #define HAVE_SYS_TYPES_H 1

(similar macros)

| /* end confdefs.h.  */
| #include <netinet/tcp.h>
| 
| int
| main ()
| {
| static struct tcp_info ac_aggr;
| if (ac_aggr.tcpi_unacked)
| return 0;
|   ;
|   return 0;
| }