netlink: dissect errors and more flags, improve display and help

netlink: dissect errors and more flags, improve display and help

Print "Protocol-specific" instead of "Unknown (0x0016)" for the type
since its interpretation depend on the subprotocol.

Dissect struct nlmsgerr (refactor and reuse the header dissection code).
Dissect Dump interrupted and Dump filtered flags.

Adjust field descriptions and value_string based on the netlink(7)
manual and linux/netlink.h. Display Flags as hex instead of decimal.
Expanded inline tabs, renamed netlink.hdr_flags.match_all to
netlink.hdr_flags.match for consistency.

Change-Id: If2b5c8d2b68fd94e70d1d8b98e63171b42b0d65c
Reviewed-on: https://code.wireshark.org/review/16932
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Peter Wu <peter@lekensteyn.nl>