Merge remote branch 'origin/tmp/k3.0_sr_backports' into sr_3.0

Merge remote branch 'origin/tmp/k3.0_sr_backports' into sr_3.0

statistics callback support (enabled only if compiled with
-DUSE_CORE_STATS) and latest kamailio 3.0 fixes

* origin/tmp/k3.0_sr_backports:
  core: new param to give outbut buffer size
  core: use one buffer for int2str
  core: use dlflags to load modules
  uac(k): use header types for detection
  uac(k): proper test for send failure
  uac(k): set type for tm callback
  core: stats events cbs are called only if USE_CORE_STATS is defined
  update drp_reqs statistics
  update drp_rpls statistics
  update fwd_rpls statistics
  update err_reqs statistics
  update err_rpls statistics
  update bad_URIs statistics
  update bad_msg_hdr statistics
  core: update fwd_reqs stat
  kex: support to update core stats via core events
  core: added new event SREV_CORE_STATS