- fix the run_enb_ue_virt_s1 script
  - change the Ki value back to the one used

thanks to Supreeth Herle for reporting.

libxslt1-dev is used at least for asn1 and usrp. It breaks the build when in
check_install_additional_tools().
Move it to to check_install_oai_software()

uhd is not part of ubuntu standard repositories >= 14.04.
Move the removal of uhd in its own space and do not fail if it doesn't exists.

clang have changed its default standard to C11 compilation and is stricter.
Ensure use of gnu89 standard to use pthread extension for --castxml-gccxml

It can't link because nas_config.c and rb_config.c was commented.