sysutils/openipmi: resolve build issues with 2.0.21

• Return EAGAIN errno instead of EKEYREJECTED to fix build with SSL option [1]
• Prepend -I../include to CPPFLAGS to stop build breakage from old .h files [2]
• While here, add LICENSE and regen one of the original patches (portlint)

PR: 202002 [1]
PR: 202528 [2]
Submitted by: dennis.noordsij@helsinki.fi [1]
Submitted by: Anton Sayetsky <vsasjason@gmail.com> [1]
Submitted by: Larry Rosenman <ler@lerctr.org> [2]
Approved by: feld (mentor)
Differential Revision: https://reviews.freebsd.org/D3568