security/softether5: set the appropreate build number

Despite the build number is a monotonically increasing value and never
decreased or reset to zero, upstream accidentaly reset it to zero.

As a result, The older version of SoftEtherVPN client cannot to
connect to 5.x developer version server. To restore compatibility,
this commit sets the appropreate build number. See also the upstream
GitHub issue.

While here, define LIB_DEPENDS pointed out by poudriere QA-test.

Obtained from: https://github.com/SoftEtherVPN/SoftEtherVPN/issues/1392#issuecomment-867348281