freebsd: Fixes for the compilation of libosmocore on FreeBSD

alloca.h is not available on FreeBSD, use the default autoconf
function to check for it, there is a complete list[1] of what to
do for using alloca but let us see how far we get with this test.

Include netinet/in.h for the IPv4 and IPv6 socket address. Check
for dlopen in libraries and use this instead of linking -dl.

[1] http://www.gnu.org/s/hello/manual/autoconf/Particular-Functions.html
4 files changed