main/openrc: fix parsing quoted kernel options in firstboot

Quoted kernel options in /proc/cmdline look like this:

modules=something "ssh_key=ssh-rsa foobar user@foo" quiet

Without the eval this would be parsed as: opt='modules=something'
opt='"ssh_key=ssh-rsa' opt='foobar' opt='user@foo"' opt='quiet'

With the eval in this branch the options are parsed correctly.

Since ssh keys need spaces and therefor must be quoted, passing ssh_key
by kernel option cannot work as currently implemented.

fixes #9504
7 jobs for !8475 with fix-ssh_key in 1 minute and 48 seconds
detached
Status Job ID Name Coverage
  Lint
failed #129304
docker-alpine x86_64 allowed to fail
lint

00:00:23

 
  Build
passed #129309
docker-alpine ci-build aarch64
build-aarch64

00:00:39

passed #129310
docker-alpine ci-build armv7
build-armv7

00:00:50

passed #129308
docker-alpine ci-build ppc64le
build-ppc64le

00:01:23

passed #129307
docker-alpine ci-build s390x
build-s390x

00:00:44

passed #129306
docker-alpine ci-build x86
build-x86

00:00:28

passed #129305
docker-alpine ci-build x86_64
build-x86_64

00:00:33

 
Name Stage Failure
failed
lint Lint
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