The flexresp is not enable for default.
I ran command rpmbuild -ba snort.spec -with mysql -with flexresp
and I have received follow message
checking for libnet version 1.0.2a... no
ERROR! Snort with --enable-flexresp will *only* work with libnet version 1.0.2a, go get it from http://www.packetfactory.net/projects/libnet/
What version of Snort are you trying to build and where did you get the source file, snort.org or from somewhere else?