apparmor: simplify IoctlRequestBuffer #293

Job	Run time
cache-build-deps	1m 39s
snap-builds	0s
static-checks (1.18)	6m 49s
static-checks (latest/stable)	8m 42s
unit-tests (1.18, normal)	7m 45s
unit-tests (1.18, snapd_debug)	9m 19s
unit-tests (1.18, withbootassetstesting)	7m 27s
unit-tests (1.18, nosecboot)	9m 11s
unit-tests (1.18, faultinject)	8m 56s
unit-tests (latest/stable, normal)	9m 34s
unit-tests (latest/stable, snapd_debug)	9m 47s
unit-tests (latest/stable, withbootassetstesting)	8m 28s
unit-tests (latest/stable, nosecboot)	10m 47s
unit-tests (latest/stable, faultinject)	7m 54s
code-coverage	6s
spread-nested	0s
spread	0s
	1h 46m 24s

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