Fix detection of DLT_* macros

[h3xx]

pcap.h in its entirety must be included in order for bpf.h to work properly.

Example test program, compiler output:

#include <stdio.h>
#include <pcap/bpf.h>

int main(void) {
#ifdef DLT_IEEE802_11
    printf("Yes\n");
#endif
}

Output:

In file included from t.c:2:
/usr/include/pcap/bpf.h:97:9: error: unknown type name 'u_int'
   97 | typedef u_int bpf_u_int32;
      |         ^~~~~
/usr/include/pcap/bpf.h:117:9: error: unknown type name 'u_int'
  117 |         u_int bf_len;
      |         ^~~~~
/usr/include/pcap/bpf.h:245:9: error: unknown type name 'u_short'
  245 |         u_short code;
      |         ^~~~~~~
/usr/include/pcap/bpf.h:246:9: error: unknown type name 'u_char'
  246 |         u_char  jt;
      |         ^~~~~~
/usr/include/pcap/bpf.h:247:9: error: unknown type name 'u_char'
  247 |         u_char  jf;
      |         ^~~~~~
/usr/include/pcap/bpf.h:271:10: error: unknown type name 'u_int'
  271 | PCAP_API u_int  bpf_filter(const struct bpf_insn *, const u_char *, u_int, u_int);
      |          ^~~~~
/usr/include/pcap/bpf.h:271:59: error: unknown type name 'u_char'
  271 | PCAP_API u_int  bpf_filter(const struct bpf_insn *, const u_char *, u_int, u_int);
      |                                                           ^~~~~~
/usr/include/pcap/bpf.h:271:69: error: unknown type name 'u_int'; did you mean 'int'?
  271 | PCAP_API u_int  bpf_filter(const struct bpf_insn *, const u_char *, u_int, u_int);
      |                                                                     ^~~~~
      |                                                                     int
/usr/include/pcap/bpf.h:271:76: error: unknown type name 'u_int'; did you mean 'int'?
  271 | PCAP_API u_int  bpf_filter(const struct bpf_insn *, const u_char *, u_int, u_int);
      |                                                                            ^~~~~
      |                                                                            int

Changing the example program to include only pcap.h works.

Linux x86_64
libpcap 1.10.4
gcc 13.1.0

[h3xx]

Also, at some point, these macros were moved to pcap/dlt.h.