selftests: defer: Allow spaces in arguments of deferred commands

selftests: defer: Allow spaces in arguments of deferred commands

Currently the way deferred commands are stored and invoked causes any
whitespace to act as an argument separator when the command is executed.
To make it possible to use spaces in deferred commands, store the commands
quoted, and then eval the string prior to execution.

Fixes: a6e263f125cd ("selftests: net: lib: Introduce deferred commands")
Signed-off-by: Petr Machata <petrm@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/6c2523139a6f99103889c9c9fedcdc66a75441f4.1757004393.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>