rds: Fix endianness annotations for RDS extension headers

rds: Fix endianness annotations for RDS extension headers

Per the RDS 3.1 spec [1], RDS extension headers EXTHDR_NPATHS and
EXTHDR_GEN_NUM are be16 and be32 values respectively, exchanged during
normal operations over-the-wire (RDS Ping/Pong). This contrasts their
declarations as host endian unsigned ints.

Fix the annotations across occurrences. Flagged by Sparse.

[1] https://oss.oracle.com/projects/rds/dist/documentation/rds-3.1-spec.html

Signed-off-by: Ujwal Kundur <ujwal.kundur@gmail.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Link: https://patch.msgid.link/20250820175550.498-5-ujwal.kundur@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>