Relax the config of add-path send and rde evaluate all

Relax the config of add-path send and rde evaluate all

add-path send is kind of like rde evaluate all (at least if plus is used)
and so it kind of implies 'rde evaluate all' in that case. Removing the
check in neighbor_consistent() allows to setup sessions so that 'either or'
are used. This makes sense since peers may opt out of add-path by disabling
the capability on their side.
Based on report from Pier Carlo Chiodi
OK tb@
cvs: ----------------------------------------------------------------------