libpcap: Fix build when PACKAGECONFIG ipv6 is not enabled

libpcap: Fix build when PACKAGECONFIG ipv6 is not enabled

Add patches provided upstream [1] by Fabio Berton to fix error:

> ./gencode.c: In function 'pcap_compile':
> ./gencode.c:693:8: error: 'compiler_state_t {aka struct _compiler_state}' has no member named 'ai'
>   cstate.ai = NULL;
>         ^
> ./gencode.c: In function 'gen_gateway':
> ./gencode.c:4914:13: error: 'cstate' undeclared (first use in this function)
>    bpf_error(cstate, "direction applied to 'gateway'");
>              ^

[1] https://github.com/the-tcpdump-group/libpcap/pull/541

Signed-off-by: Fabio Berton <fabio.berton@ossystems.com.br>
Tested-by: Zefir Kurtisi <zefir.kurtisi@neratec.com>