jvpp: do not hardcode event sufixes (VPP-940)

jvpp: do not hardcode event sufixes (VPP-940)

JVpp maps request messages with replies
for Java API user convenience, e.g.:
- do not polute send APIs with messages other than requests/dumps,
- allow callback registration only for replies/details and events.

Since there are no conventions for event message naming
(https://wiki.fd.io/view/VPP/API_Concepts#API_Conventions),

jvpp should not limit events to messages
that end with 'event' or 'counters' suffix.

Instead jvpp should treat all messages
except for requests/dumps as potential events.

Such behaviour was introduced on Java API level by
https://gerrit.fd.io/r/#/c/8377/

in order support reusing
details messages as events (e.g. BFD events).

This patch goes one step forward by
relaxing rules at jvpp generation level.

Change-Id: I2a35e9eb2a288b2cf02d36ca95e6cb13e76e19e3
Signed-off-by: Marek Gradzki <mgradzki@cisco.com>