Add optional options= argument to Listen to add listener-specific

Add optional options= argument to Listen to add listener-specific
socket options.

Reimplement "use_specific_errors" listener flag under generic
ap_listen_rec flags field holding all listener-specific options.

* include/ap_listen.h: Add AP_LISTEN_* flags.
  (ap_listen_rec): Rename use_specific_errors to flags.

* server/listen.c (make_sock): Set APR_SO_FREEBIND if
  AP_LISTEN_FREEBIND flag is set on listener; set APR_SO_REUSEPORT
  unconditionally if AP_LISTEN_REUSEPORT is set.
  (alloc_listener): Take flags argument.
  (ap_setup_listeners): Set AP_LISTEN_SPECIFIC_ERRORS flag here.
  (ap_set_listener): Parse optional options=... argument, catch
  typos and fail if protocol name contains a "=".
  (ap_duplicate_listeners): Duplicate flags.

Submitted by: jkaluza, Lubos Uhliarik <luhliari redhat.com>, jorton
PR: 61865
Github: closes #114

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1876865 13f79535-47bb-0310-9956-ffa450edef68