'const fooPtr' is the same as 'foo * const' (the pointer won't
change, but it's contents can).  But in general, if an interface
is trying to be const-correct, it should be using 'const foo *'
(the pointer is to data that can't be changed).

Fix up offenders in nwfilter code.

This patch does nothing about the stupidity evident in having
__virNWFilterInstantiateFilter, _virNWFilterInstantiateFilter,
and virNWFilterInstantiateFilter, which differ only by leading
underscores, and which infringes on the namespace reserved to
the implementation - that would need to be a separate cleanup.

* src/nwfilter/nwfilter_dhcpsnoop.h (virNWFilterDHCPSnoopReq): Use
intended type.
* src/nwfilter/nwfilter_gentech_driver.h
(virNWFilterInstantiateFilter)
(virNWFilterUpdateInstantiateFilter)
(virNWFilterInstantiataeFilterLate, virNWFilterTeardownFilter)
(virNWFilterCreateVarHashmap): Likewise.
* src/nwfilter/nwfilter_learnipaddr.h (virNWFilterLearnIPAddress):
Likewise.
* src/conf/nwfilter_conf.h (virNWFilterApplyBasicRules)
(virNWFilterApplyDHCPOnlyRules): Likewise.
(virNWFilterDefFormat): Make const-correct.
* src/conf/nwfilter_params.h (virNWFilterVarValueCopy)
(virNWFilterVarValueGetSimple, virNWFilterVarValueGetCardinality)
(virNWFilterVarValueEqual, virNWFilterVarAccessEqual)
(virNWFilterVarAccessGetVarName, virNWFilterVarAccessGetType)
(virNWFilterVarAccessGetIterId, virNWFilterVarAccessGetIndex)
(virNWFilterVarAccessIsAvailable)
(virNWFilterVarCombIterGetVarValue): Use intended type.
(virNWFilterVarValueGetNthValue): Make const-correct.
* src/nwfilter/nwfilter_dhcpsnoop.c (virNWFilterSnoopReqLeaseDel)
(virNWFilterSnoopIFKeyFMT, virNWFilterDHCPSnoopReq)
(virNWFilterSnoopPruneIter, virNWFilterSnoopRemAllReqIter)
(virNWFilterDHCPSnoopReq): Fix fallout.
* src/nwfilter/nwfilter_gentech_driver.c
(virNWFilterVarHashmapAddStdValues, virNWFilterCreateVarHashmap)
(virNWFilterInstantiate, __virNWFilterInstantiateFilter)
(_virNWFilterInstantiateFilter, virNWFilterInstantiateFilterLate)
(virNWFilterInstantiateFilter)
(virNWFilterUpdateInstantiateFilter)
(virNWFilterRollbackUpdateFilter, virNWFilterTeardownFilter):
Likewise.
* src/nwfilter/nwfilter_learnipaddr.c (virNWFilterLearnIPAddress):
Likewise.
* src/conf/nwfilter_params.c (virNWFilterVarValueCopy)
(virNWFilterVarValueGetSimple)
(virNWFilterVarValueGetCardinality, virNWFilterVarValueEqual)
(virNWFilterVarCombIterAddVariable)
(virNWFilterVarCombIterGetVarValue, virNWFilterVarValueCompare)
(virNWFilterFormatParamAttributes, virNWFilterVarAccessEqual)
(virNWFilterVarAccessGetVarName, virNWFilterVarAccessGetType)
(virNWFilterVarAccessGetIterId, virNWFilterVarAccessGetIndex)
(virNWFilterVarAccessGetIntIterId)
(virNWFilterVarAccessIsAvailable)
(virNWFilterVarValueGetNthValue): Likewise.
* src/nwfilter/nwfilter_ebiptables_driver.c (ebtablesApplyBasicRules)
(ebtablesApplyDHCPOnlyRules, ebiptablesRuleOrderSort)
(ebiptablesRuleOrderSortPtr): Likewise.
* src/conf/nwfilter_conf.c (virNWFilterDefEqual)
(virNWFilterDefFormat): Likewise.
Signed-off-by: NEric Blake <eblake@redhat.com>