common/pick_address: conditional compile for crimson

common/pick_address: conditional compile for crimson

crimson can only update configuration async, so we cannot let
pick_addreses() call set_val_or_die() without chaning its function
signature.

for implementing crimson-osd, what we need is only a single
pick_addresses() variant, which returns entity_addrvec_t. so we just
enable it if WITH_SEASTAR is defined instead of adding a wrapper or
reimplement all pick_addresses() variants for crimson-osd.

Signed-off-by: Kefu Chai <kchai@redhat.com>