concurrent map reading master offset map in linuxptpdaemon

ptp4l[2176528.677]: [ptp4l.0.config] rms    2 max    5 freq -11753 +/-   3 delay    83 +/-   1
fatal error: concurrent map read and map writegoroutine 123 [running]:
runtime.throw({0x15f4c8a?, 0x13c1ae0?})
    /usr/local/go/src/runtime/panic.go:992 +0x71 fp=0xc000197b60 sp=0xc000197b30 pc=0x438bb1
runtime.mapaccess2_faststr(0x13c1ae0?, 0xc0003593a0?, {0xc0003f8d20, 0xe})
    /usr/local/go/src/runtime/map_faststr.go:117 +0x3d4 fp=0xc000197bc8 sp=0xc000197b60 pc=0x414b14
github.com/openshift/linuxptp-daemon/pkg/daemon.getMasterOffsetIfaceName(...)
    /go/src/github.com/openshift/linuxptp-daemon/pkg/daemon/metrics.go:501
github.com/openshift/linuxptp-daemon/pkg/daemon.extractSummaryMetrics({0xc0003f8d20, 0xe}, {0x15d63a4, 0x5}, {0xc000460ea0, 0x5e})
    /go/src/github.com/openshift/linuxptp-daemon/pkg/daemon/metrics.go:257 +0x336 fp=0xc000197da0 sp=0xc000197bc8 pc=0x12fdaf6
github.com/openshift/linuxptp-daemon/pkg/daemon.extractMetrics({0xc0003f8d20, 0xe}, {0x15d63a4, 0x5}, {0xc00004c3c0, 0x2, 0x1?}, {0xc000460ea0, 0x5e})
    /go/src/github.com/openshift/linuxptp-daemon/pkg/daemon/metrics.go:177 +0xc5 fp=0xc000197f20 sp=0xc000197da0 pc=0x12fd0e5
github.com/openshift/linuxptp-daemon/pkg/daemon.cmdRun.func2()
    /go/src/github.com/openshift/linuxptp-daemon/pkg/daemon/daemon.go:457 +0x96 fp=0xc000197fe0 sp=0xc000197f20 pc=0x12fbfd6
runtime.goexit()
    /usr/local/go/src/runtime/asm_amd64.s:1571 +0x1 fp=0xc000197fe8 sp=0xc000197fe0 pc=0x468aa1
created by github.com/openshift/linuxptp-daemon/pkg/daemon.cmdRun
    /go/src/github.com/openshift/linuxptp-daemon/pkg/daemon/daemon.go:451 +0x60a

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