minor, wrap context in ud-ping.c into a ctx_s struct and pass that around

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
cosmetics, use %d and int cast for PONG's pid (instead of %jd and intmax_t cast)

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, support -c|--count argument to ud-ping

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

* tool/ud-ping:
  minor, support -c|--count argument to ud-ping
  cosmetics, use %d and int cast for PONG's pid (instead of %jd and intmax_t cast)
  minor, wrap context in ud-ping.c into a ctx_s struct and pass that around
Merge branch 'next'

* next:
  minor, support -c|--count argument to ud-ping
  cosmetics, use %d and int cast for PONG's pid (instead of %jd and intmax_t cast)
  minor, wrap context in ud-ping.c into a ctx_s struct and pass that around
  test, provide another pubsub test with 2 packs in one message
  test, provide simple pubsub test
  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
  chore, compile tests with -DUD_NEW_API
  fix, lower ETH_MTU value to 1492, taking udp into account
  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