bpf: decouple BPF link/attach hook and BPF program sleepable semantics

BPF link's lifecycle protection scheme depends on both BPF hook and BPF
program. If *either* of those require RCU Tasks Trace GP, then we need
to go through a chain of GPs before putting BPF program refcount and
deallocating BPF link memory.

This patch adds bpf_link-specific sleepable flag, which can be set to
true even if underlying BPF program is not sleepable itself. If either
link->sleepable or link->prog->sleepable is true, we'll go through
a chain of RCU Tasks Trace GP and RCU GP before putting BPF program and
freeing memory.

This will be used to protect BPF link for sleepable (faultable) raw
tracepoints in the next patch.

Link: https://lore.kernel.org/[email protected]
Tested-by: Jordan Rife <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

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