build: rename --enable-ebpf to --enable-usdt

eBPF is a Linux kernel technology used to "extend the capabilities
of the kernel without requiring to change kernel source code or
load kernel modules". While Userspace, Statically Defined Tracing
(USDT) uses eBPF under the hood, --enable-usdt better resembles that
support for USDT is enabled, and tracepoints will be included in the
binary.

configure.ac

@@ -137,11 +137,11 @@ AC_ARG_WITH([bdb],
   [use_bdb=$withval],
   [use_bdb=auto])
 
-AC_ARG_ENABLE([ebpf],
-  [AS_HELP_STRING([--enable-ebpf],
-  [enable eBPF tracing (default is yes if sys/sdt.h is found)])],
-  [use_ebpf=$enableval],
-  [use_ebpf=yes])
+AC_ARG_ENABLE([usdt],
+  [AS_HELP_STRING([--enable-usdt],
+  [enable tracepoints for Userspace, Statically Defined Tracing (default is yes if sys/sdt.h is found)])],
+  [use_usdt=$enableval],
+  [use_usdt=yes])
 
 AC_ARG_WITH([miniupnpc],
   [AS_HELP_STRING([--with-miniupnpc],
@@ -1341,15 +1341,15 @@ if test "$enable_wallet" != "no"; then
     fi
 fi
 
-if test "$use_ebpf" != "no"; then
-  AC_MSG_CHECKING([whether eBPF tracepoints are supported])
+if test "$use_usdt" != "no"; then
+  AC_MSG_CHECKING([whether Userspace, Statically Defined Tracing tracepoints are supported])
   AC_COMPILE_IFELSE([
     AC_LANG_PROGRAM(
       [#include <sys/sdt.h>],
       [DTRACE_PROBE("context", "event");]
     )],
-    [AC_MSG_RESULT([yes]); have_sdt=yes; AC_DEFINE([ENABLE_TRACING], [1], [Define to 1 to enable eBPF user static defined tracepoints])],
-    [AC_MSG_RESULT([no]); have_sdt=no;]
+    [AC_MSG_RESULT([yes]); AC_DEFINE([ENABLE_TRACING], [1], [Define to 1 to enable tracepoints for Userspace, Statically Defined Tracing])],
+    [AC_MSG_RESULT([no]); use_usdt=no;]
   )
 fi
 
@@ -1763,7 +1763,6 @@ AM_CONDITIONAL([TARGET_WINDOWS], [test "$TARGET_OS" = "windows"])
 AM_CONDITIONAL([ENABLE_WALLET], [test "$enable_wallet" = "yes"])
 AM_CONDITIONAL([USE_SQLITE], [test "$use_sqlite" = "yes"])
 AM_CONDITIONAL([USE_BDB], [test "$use_bdb" = "yes"])
-AM_CONDITIONAL([ENABLE_TRACING], [test "$have_sdt" = "yes"])
 AM_CONDITIONAL([ENABLE_TESTS], [test "$BUILD_TEST" = "yes"])
 AM_CONDITIONAL([ENABLE_FUZZ], [test "$enable_fuzz" = "yes"])
 AM_CONDITIONAL([ENABLE_FUZZ_BINARY], [test "$enable_fuzz_binary" = "yes"])
@@ -1932,7 +1931,7 @@ echo "  with bench      = $use_bench"
 echo "  with upnp       = $use_upnp"
 echo "  with natpmp     = $use_natpmp"
 echo "  use asm         = $use_asm"
-echo "  ebpf tracing    = $have_sdt"
+echo "  USDT tracing    = $use_usdt"
 echo "  sanitizers      = $use_sanitizers"
 echo "  debug enabled   = $enable_debug"
 echo "  gprof enabled   = $enable_gprof"