This pull request adds support for Ubuntu 22.04 in BESS. Fixes #1056. Overview of the changes made:

• Fixed g++-11 (default in Ubuntu 22.04) warnings in core/modules/l2_forward.cc (-Werror=maybe-uninitialized), core/utils/exact_match_table.h (-Werror=nonnull).
• Updated DPDK 19.11 for newer kernels (Ubuntu 22.04 uses either 5.15 or 6.8 by default):
  • deps/linux_5_9.patch: Kernel v5.9 removed the task_struct pointer from get_user_pages_remote. Updated kernel/linux/kni/kni_dev.h with newer get_user_pages_remote and fixed a fallthrough warning (-Wimplicit-fallthrough) in kernel/linux/igb/igb_uio.c.
  • build.py: Now checking for version greater than or equal to 5.9 and applying the above patch. These changes depend on the packaging module in python3.
• Upgraded to python3 (default in Ubuntu 22.04):
  • bessctl/sugar.py: parser module is not present in python v3.10. Made changes to use the ast module instead.
• Updated core/Makefile: Now linking libpcap, and libgrpc++ dynamically. Statically linking them results in issues due to change in dependencies in Ubuntu 22.04. libpcap depends on libdbus and libsystemd. libsystemd does not have a static library as part of its package. Linking libgrpc++ statically results in unresolved libssl symbols, potentially due to a version mismatch in Ubuntu 22.04's libssl and the one libgrpc++ was written with.
• Modified core/kmod/sn_ethtool.c to include ethtool.h for struct ethtool_drvinfo. While the code compiles successfully on older kernel versions (Ubuntu 18.04) without this include, Ubuntu 22.04 reports 'invalid use of undefined type struct ethtool_drvinfo'. Now including ethtool.h explicitly rather than relying on transitive includes.