header: add sk_set_bit() and sk_clear_bit()

This adds the sk_set_bit() and sk_clear_bit() functions in addition to
the renaming of SOCK_ASYNC_NOSPACE and SOCK_ASYNC_WAITDATA. This is
needed since upstream commit 9cd3e072

 "net: rename
SOCK_ASYNC_NOSPACE and SOCK_ASYNC_WAITDATA"

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>