chore, invert the guards, use UD_NEW_API to explicitly enable the new API

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
chore, compile libunserding with UD_NEW_API and UD_COMPAT

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
chore, compile unsermon and ud-ping with -DUD_NEW_API

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'bld/dist' into next

* bld/dist:
  chore, compile unsermon and ud-ping with -DUD_NEW_API
  chore, compile libunserding with UD_NEW_API and UD_COMPAT
  chore, invert the guards, use UD_NEW_API to explicitly enable the new API
fix, lower ETH_MTU value to 1492, taking udp into account

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'core/api' into next

* core/api:
  fix, lower ETH_MTU value to 1492, taking udp into account
chore, compile tests with -DUD_NEW_API

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'bld/dist' into next

* bld/dist:
  chore, compile tests with -DUD_NEW_API
minor, make ud_chck_cmsg() return to caller without setting TGT

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, make ud_chck_msg() call ud_chck_cmsg() for control messages and proceed normally after callee returns

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
chore, doc, put some explanations in front of ud_{pack,chck}_cmsg() and ud_chck_aux()

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
hygiene, assume control messages are unlikely

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
fix, PEBKAC, when setting nck slot of __sock_t take length and type indicator into account

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
fix, PEBKAC, always set the service slot upon ud_pack_msg()

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'core/api' into next

* core/api:
  fix, PEBKAC, always set the service slot upon ud_pack_msg()
  fix, PEBKAC, when setting nck slot of __sock_t take length and type indicator into account
  hygiene, assume control messages are unlikely
  chore, doc, put some explanations in front of ud_{pack,chck}_cmsg() and ud_chck_aux()
  minor, make ud_chck_msg() call ud_chck_cmsg() for control messages and proceed normally after callee returns
  minor, make ud_chck_cmsg() return to caller without setting TGT
test, provide simple pubsub test

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
test, provide another pubsub test with 2 packs in one message

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'test/general' into next

* test/general:
  test, provide another pubsub test with 2 packs in one message
  test, provide simple pubsub test