Docs: flex and byacc as required packages for libpcap in build.md (#1189)

Docs: flex and byacc as required packages for libpcap in build.md

In order to run `./configure` in `libpcap (1.2.2.)`, `flex` or `lex` and
`yacc/byacc` must be installed.

Tested on Ubuntu 22.04.5 LTS.

```text
$ sudo apt update -y 
$ sudo apt install -y git flex byacc yacc
$ git clone https://github.com/the-tcpdump-group/libpcap.git -b libpcap
$ cd libpcap
$ ./configure
```

Author: MateuszGrabuszynski

doc/build.md

@@ -12,7 +12,7 @@ Please note that the DPDK dependency remains necessary when utilizing the XDP/ke
 
 ```bash
 sudo apt-get update
-sudo apt-get install git gcc meson python3 python3-pip pkg-config libnuma-dev libjson-c-dev libpcap-dev libgtest-dev libssl-dev systemtap-sdt-dev llvm clang
+sudo apt-get install git gcc meson python3 python3-pip pkg-config libnuma-dev libjson-c-dev libpcap-dev libgtest-dev libssl-dev systemtap-sdt-dev llvm clang flex byacc
 sudo pip install pyelftools ninja
 ```