This commit brings many minor fixes to the documentation for BPF helper
functions. Mostly, this is limited to formatting fixes and improvements.
In particular, fix broken formatting for bpf_skb_adjust_room().

Besides formatting, replace the mention of "bpf_fullsock()" (that is not
associated with any function or type exposed to the user) in the
description of bpf_sk_storage_get() by "full socket".

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>