[release-1.22] h2/fix dropper

[istio-testing]

Manual cherrypick required.

#1057 failed to apply on top of branch "release-1.22":

Applying: With compiler bug
Using index info to reconstruct a base tree...
A	src/proxy/h2.rs
A	src/proxy/h2/client.rs
A	src/proxy/h2/server.rs
Falling back to patching base and 3-way merge...
Auto-merging src/proxy/h2_client.rs
CONFLICT (content): Merge conflict in src/proxy/h2_client.rs
CONFLICT (modify/delete): src/proxy/h2/server.rs deleted in HEAD and modified in With compiler bug. Version With compiler bug of src/proxy/h2/server.rs left in tree.
CONFLICT (modify/delete): src/proxy/h2/client.rs deleted in HEAD and modified in With compiler bug. Version With compiler bug of src/proxy/h2/client.rs left in tree.
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 With compiler bug
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

[howardjohn]

actually this only impacts master branch unless we take fd2da17