af-binder: Extend maxlength of websocket messages

af-binder: Extend maxlength of websocket messages

The default maxlength of 65000 bytes is too limited.
This commit extends the maxlength to 1048500 bytes.

Also includes minor improvements and fixes.

Bug-AGL: SPEC-981

Change-Id: Ic891ae90bbdd5ec94310bfc3aea1fb30f6e80077
Signed-off-by: José Bollo <jose.bollo@iot.bzh>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/11491
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-boot-test: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.com>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>