telemetry: fix build with gcc 9

telemetry: fix build with gcc 9

Suppress the unaligned packed member address warnings by extending
the telemetry library build flags with -Wno-address-of-packed-member
option, through the WERROR_FLAGS makefile variable.

With this change additional warnings are turned on to be treated as errors,
which causes the following build issues to be seen:
- no previous prototype [-Werror=missing-prototypes]
- initialization discards ‘const’ qualifier from pointer target type
  [-Werror=discarded-qualifiers]
- old-style function definition [-Werror=old-style-definition]
- variable may be used before its value is set (when using icc compiler).

Fixes: 0fe3a37924d4 ("telemetry: format json response when sending stats")
Fixes: ee5ff0d3297e ("telemetry: add client feature and sockets")
Fixes: 8877ac688b52 ("telemetry: introduce infrastructure")
Fixes: 1b756087db93 ("telemetry: add parser for client socket messages")
Fixes: fff6df7bf58e ("telemetry: fix using ports of different types")
Fixes: 4080e46c8078 ("telemetry: support global metrics")
Cc: stable@dpdk.org
Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>
Signed-off-by: Flavia Musatescu <flavia.musatescu@intel.com>
Acked-by: Kevin Laatz <kevin.laatz@intel.com>