This reverts commit 2ce6a7eb.

the Requires list contained a trailing comma if liburcu wasn't present,
pkg-config as of 0.29 treats this as an error, resulting in failed
package --cflags and --atleast-version lookups

this change treats libdnssec as mandatory, and extras must be prefixed with
comma inside the expanded variables

Revert another useless change related to version.h wizardry.

Add LIBKNOT_VERSION_HEX and rename the variables to match libuv naming convention (looks slightly better)

Add auto mode to lmdb that will fallback to embedded version if shared lmdb is too old or non-existent

Just check the first version of lmdb for a required version, since the other versions won't be used for compilation anyway reliably

The binding of multiple sockets with SO_REUSEPORT flag depends on
detecting the SO_REUSEPORT macro in system headers. It turned out
that FreeBSD has the same macro but the semantic is different.

Require Linux in autodetecion mode for enabling multiple sockets
binding.

Add support for binding multiple UDP sockets for with SO_REUSEPORT
flag in order to overcome performance hit caused by sharing one
socket and waiting on one single lock in kernel.