sofia-sip: new package

[Thomas:
 - Add better Config.in help text.
 - Fix the hash file format.
 - Fix comment header in .mk file.
 - Remove SOURCE variable, as it had the default value.
 - Add dependency on host-pkgconf, used by the configure script.
 - Add LICENSE and LICENSE_FILES variables.
 - Do not use BR2_HAVE_DOCUMENTATION, this option has been
   removed. Instead, always disable doxygen.
 - Simplify the IPv6 test.
 - Add optional dependency on OpenSSL.
 - Fixup the handling of the --enable-ndebug.]

Signed-off-by: Gregory Dymarek <gregd72002@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>