Compile using mock:
wget http://downloads.asterisk.org/pub/telephony/dahdi-linux/dahdi-linux-2.11.1.tar.gz
mock --resultdir=. -r nethserver-7-x86_64 -D 'dist .ns7' -D 'version 2.11.1' -D 'release 3.10.0_862.el7' --buildsrpm --spec dahdi-linux-kmod.spec --sources .
mock --resultdir=. -r nethserver-7-x86_64 -D 'dist .ns7' -D 'version 2.11.1' -D 'release 3.10.0_862.el7' dahdi-linux-kmod-*.src.rpm
If you need to increase the current spec release, add it to the dist tag:
-D 'dist .1.ns7'