lwIP 2.1.2 is now available from the lwIP download area on savannah 
or via git (using the STABLE-2_1_2_RELEASE tag).
This is an even smaller bugfix-only release fixing 4 bugs (see
CHANGELOG). However, 2 of them are in the core TCP code, so all users of
2.1.0 or 2.1.1 are*strongly*suggested to upgrade (should be a matter of
copying the new files only, no changes required)!