Fix unused variable warnings in sctp_indata.c
With clang 15, the following -Werror warnings are produced:
sys/netinet/sctp_indata.c:3309:6: error: variable 'tot_retrans' set but not used [-Werror,-Wunused-but-set-variable]
int tot_retrans = 0;
^
sys/netinet/sctp_indata.c:3842:20: error: variable 'resend' set but not used [-Werror,-Wunused-but-set-variable]
int inflight = 0, resend = 0, inbetween = 0, acked = 0, above = 0;
^
sys/netinet/sctp_indata.c:3842:47: error: variable 'acked' set but not used [-Werror,-Wunused-but-set-variable]
int inflight = 0, resend = 0, inbetween = 0, acked = 0, above = 0;
^
sys/netinet/sctp_indata.c:3842:58: error: variable 'above' set but not used [-Werror,-Wunused-but-set-variable]
int inflight = 0, resend = 0, inbetween = 0, acked = 0, above = 0;
^The 'tot_retrans' variable was used in sctp_strike_gap_ack_chunks(), but
refactoring in 493d8e5a830e got rid of it. Remove the variable since it
no longer serves any purpose.
The 'resend', 'acked', and 'above' variables are only used when
INVARIANTS is undefined. Ensure they are only declared and set in that
case.
MFC after: 3 days
(cherry picked from commit 05b3a4282c408f495add570bbca12242dd006279)