libpcap: Update to version 1.8.1

libpcap: Update to version 1.8.1

  - Option --enable-canusb was removed on commit:
    https://github.com/the-tcpdump-group/libpcap/commit/93ca5ff7030aaf1219e1de05ec89a68384bfc50b
  - Autotools class was improved and we can now stop aclocal from running at all.
  - File configure.in was renamed to configure.ac, rework libpcap-pkgconfig-support
    patch and do_configure_prepend task to use configure.ac file.

Signed-off-by: Fabio Berton <fabio.berton@ossystems.com.br>
Signed-off-by: Ross Burton <ross.burton@intel.com>