ktls: make ktls_disable_ifnet() shim static

A user reported that when compiling without KERN_TLS, and
with -O0, the kernel failed to link due to ktls_disable_ifnet()
being undefined.   Making the shim static works around this issue.

Reported by: Gary Jennejohn
Sponsored by: Netflix

sys/sys/ktls.h

@@ -238,7 +238,7 @@ extern unsigned int ktls_ifnet_max_rexmit_pct;
 void ktls_disable_ifnet(void *arg);
 #else
 #define ktls_ifnet_max_rexmit_pct 1
-inline void
+static inline void
 ktls_disable_ifnet(void *arg __unused)
 {
 }