bpf: Check active lock count in in_sleepable_context()

bpf: Check active lock count in in_sleepable_context()

The in_sleepable_context() function is used to specialize the BPF code
in do_misc_fixups(). With the addition of nonsleepable arena kfuncs,
there are kfuncs whose specialization depends on whether we are
holding a lock. We should use the nonsleepable version while
holding a lock and the sleepable one when not.

Add a check for active_locks to account for locking when specializing
arena kfuncs.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260106-arena-under-lock-v2-1-378e9eab3066@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>