s4-loadparm: change lp_*() to lpcfg_*() and provide s3 compatibility lp_*()

s4-loadparm: change lp_*() to lpcfg_*() and provide s3 compatibility lp_*()

This patch changes all Samba4 loadparm functions that take a
loadparm_context or a loadparm_service structure to use a lpcfg_*()
prefix. It then creates lp_*() functions which are wrappers around the
lpcfg_*() functions. This should allow us to mix Samba3 and Samba4
code which uses loadparm calls.

This first patch just makes the manual changes to the core loadparm
code. The tree will not build with just this patch. The next patch
replaces all of the callers, and was generated automatically with a
perl script.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>