ip-address: Fix filtering by negated address flags

ip-address: Fix filtering by negated address flags

When disabling a flag, one needs to AND with the inverse not the flag
itself. Otherwise specifying for instance 'home -nodad' will effectively
clear the flags variable.

While being at it, simplify the code a bit by merging common parts of
negated and non-negated case branches. Also allow for the "special
cases" to be inverted, too.

Fixes: f73ac674d0abf ("ip: change flag names to an array")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>