mb_reclaim() calls the protocol drain routines for each protocol in each domain. Some protocols exist in more than one domain and share drain routines. In the case of SCTP, it also uses the same drain routine for its SOCK_SEQPACKET and SOCK_STREAM entries in the same domain.

On systems with INET, INET6, and SCTP all defined, mb_reclaim() calls sctp_drain() four times. On systems with INET and INET6 defined, mb_reclaim() calls tcp_drain() twice.

Eliminate this duplication by ensuring that each pr_drain routine is only specified for one protocol entry in one domain.