Add support for rc.conf(5) initialisation.

Provide user support for rc.conf(5) so a user can create a suitable
/etc/rc.conf file to initialise libbsd.

This patch by default adds basic networking support:

 cloned_interfaces
 ifconfig_'interface'
 defaultrouter
 hostname

Refer to FreeBSD documentation for examples.

Users can make a single call to have /etc/rc.conf processed, or pass a
file name to a specific configuration file or a text string with line
feeds can be passed to the scripting version of the interface.

The rc.conf support is implemented in terms of directive handlers that
are called based on a regular expression. The design allows new handlers
to be added as needed.

Line concatenation is still to be implemented.

libbsd.py

@@ -63,6 +63,8 @@ def rtems(mm):
             'rtems/rtems-bsd-get-mac-address.c',
             'rtems/rtems-bsd-get-task-priority.c',
             'rtems/rtems-bsd-get-task-stack-size.c',
+            'rtems/rtems-bsd-rc-conf-net.c',
+            'rtems/rtems-bsd-rc-conf.c',
             'rtems/rtems-bsd-shell.c',
             'rtems/rtems-bsd-shell-netcmds.c',
             'rtems/rtems-bsd-syscall-api.c',
@@ -2449,6 +2451,7 @@ def tests(mm):
     mod.addTest(mm.generator['test']('vlan01', ['test_main'], netTest = True))
     mod.addTest(mm.generator['test']('lagg01', ['test_main'], netTest = True))
     mod.addTest(mm.generator['test']('log01', ['test_main']))
+    mod.addTest(mm.generator['test']('rcconf01', ['test_main']))
     return mod
 
 #