Fix missing include pcap/pcap.h in input raw plugin

[jirutka]

Fixes the following error when building with gcc 15 on Alpine Linux:

In file included from src/plugins/input/raw/src/raw.cpp:15:
src/plugins/input/raw/src/raw.hpp:153:6: error: variable or field 'packet_handler' declared void
  153 | void packet_handler(u_char* arg, const struct pcap_pkthdr* h, const u_char* data);
      |      ^~~~~~~~~~~~~~
src/plugins/input/raw/src/raw.hpp:153:21: error: 'u_char' was not declared in this scope; did you mean 'putchar'?
  153 | void packet_handler(u_char* arg, const struct pcap_pkthdr* h, const u_char* data);
      |                     ^~~~~~
      |                     putchar
src/plugins/input/raw/src/raw.hpp:153:29: error: 'arg' was not declared in this scope
  153 | void packet_handler(u_char* arg, const struct pcap_pkthdr* h, const u_char* data);
      |                             ^~~
src/plugins/input/raw/src/raw.hpp:153:34: error: expected primary-expression before 'const'
  153 | void packet_handler(u_char* arg, const struct pcap_pkthdr* h, const u_char* data);
      |                                  ^~~~~
src/plugins/input/raw/src/raw.hpp:153:63: error: expected primary-expression before 'const'
  153 | void packet_handler(u_char* arg, const struct pcap_pkthdr* h, const u_char* data);
      |                                                               ^~~~~