Build-depend on libbsd-dev and libelf-dev

Allows to use external dependencies rather than inline versions of
library functions, so that we don't have to worry about security
issues and so on.

Change-Id: I313f94d0ed82766caab5d84a690d2ffea4ac771b
Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>

debian/control

@@ -10,7 +10,9 @@ Build-Depends: debhelper (>= 10),
                doxygen <!nodoc>,
                graphviz <!nodoc>,
                inkscape <!nodoc>,
+               libbsd-dev,
                libcap-dev,
+               libelf-dev,
                libibverbs-dev,
                libipsec-mb-dev [amd64],
                libpcap-dev,