http: fix missing imports

fixes regression introduces by davix fis backport

Acked-by:
Target: 2.7, 2.6
Require-book: no
Require-notes: no
(cherry picked from commit 581400eed0b20ddbf06ceb7337efbd804cb5e9e6)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #645 from kofemann/fix-http-v2-2.6

http: fix missing imports